Fanfic / The Core Problem

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Luna, the deity of anarchy and revolution, desires to slay the chosen champion of her sister. However, due to their very nature, Luna would be too bored to follow a straightforward plan and wants her pawns for the gambit to attempt rebellion against her.

To that end, she copies the minds and personalities of the people of a specific world and implants those into available souls, and picks two of them to be the joint minds of a Dungeon Core. Now Izuku and Tomura must work together to build a great dungeon after being thrown into the deep end by Luna.

The Core Problem is a My Hero Academia fanfiction created by Mirrond. It can also be found here on Royal Road.

A second story, Core Problem 2: Electric Boogaloo, was also created on Archive, presenting a cast that is more divested from MHA. In this version, the two dungeon masters are Revenant, an SSS-class villain who takes Tomura's role, and Analyst, a first-year hero student who replaces Izuku.

This fanfic contains examples of:

• Abled in the Adaptation: Compress regains the arm Overhaul destroyed post-isekai.
• Actually Pretty Funny:
  • Izuku admits that Tomura calling All for One's level of edgelord pizza-cutter level, as in, all edge and no point, to be an actually good insult.
  • One of Keran's friends says he's been thinking, which prompts another friend to say it's a new experience for him, which gets even the butt of the joke laughing.
• Adaptational Superpower Change: All Quirks are lost upon the transfer to the new world.
• Adaptation Personality Change: After being forced into a fantasy world, Izuku turns towards being very snarky with Tomura as a coping mechanism.
• Adaptation Relationship Overhaul: Due to being forcefully taken from their world and placed in the new one, the characters previous conflicts in the canon of My Hero Academia are rendered largely meaningless and most see it as a fresh start.
• Ambiguous Situation: Did Anaya and Gaius have a steamy affair as the latter claimed or was it made up like Anaya said? Gaius acts like a casanova but his flirting with Anaya all get handily rejected by her. However, outside of this one thing, he doesn't really fit the template of casanova wannabes since he is otherwise competent at the job of being a high priest, and is appropriately diplomatic to other parties. The truth is unclear, and while Tomura is curious about the answer, Izuku would prefer not knowing.
• Anti-Frustration Features: Izuku and Tomura figure out that in Luna's gacha system for them to redeem favours, the first few rolls for a pantheon will be for the shrines they haven't unlocked yet, to allow them a reliable way of accumulating more divine favour.
• Aren't You Going to Ravish Me?: One captured Rapturous Ecstasy prisoner is disappointed that the rape attempt on her is thwarted.
• The Assimilator: A dungeon gains more options by absorbing things within its domain.
• Attack Its Weak Point: One of the theurgies Ochako gets, Eye of Truth, lets her see an opponent's weak points, making it easy for her to target these weak points.
• Bait-and-Switch: Tomura tells Izuku that his words reached his heart and he will strive to be better. It seems like he will be a better person before he clarifies he will be a better villain.
• Battle Trophy: The Manflayers have a morbid tradition where they take the skin of their worthy defeated enemies.
• Beautiful All Along: Without his Quirk making him a lizardman, Spinner would look hot enough to be a world-renowned model.
• Best Friend: Sometime after Izuku and Ochako enter a romantic relationship, Shoto realizes that Ochako no longer qualifies as Izuku's best friend and insists on being the replacement best friend.
• Bigger on the Inside: The lodge Spinner found is discovered by Monoma to be just slightly bigger on the inside, which lets the group checking it out narrow down where the interesting things are.
• Big "NO!": Monoma shouts a big no after learning that after being isekai'd, the class rivalries don't matter anymore.
• Bizarre Alien Biology: Hamadryads bleed tree sap instead of blood.
• Blood Knight: Ay’zira the Amazon loves fighting, and Izuku thinks her attitude is representative of not just Amazons but all of the Nine Hordes daemons.
• But for Me, It Was Tuesday: Izuku is annoyed Tomura doesn't remember his name even though he threatened to kill him. Tomura responds that he threatens to kill a lot of people, and that incident with Izuku was not that special to him.
• Casanova Wannabe: Gaius claims to have had a steamy affair with Elder Anaya. Anaya claims he made that up. The truth is left ambiguous in-story.
• Clone Angst: One not-insignificant point of contention the characters have with what Luna did is that they are the copies of the original people they were. Some are more distraught by this fact than others.
• Conditioned to Accept Horror: Gaius and Anneya have seen so many horrific cults that they have started rating them on their aesthetics despite it's complete irrelevance to having to stop them.
• Counterfeit Cash: Izuku discusses with Gaius how to prevent people counterfeiting the tokens he'd be using as currency in his dungeon's territory.
• Curb-Stomp Battle:
  • When Elder Anaya, Uzar, and Yla go through Izuku's and Tomura's dungeon in Chapters 33 and 34, they steamroll over most of the things that gets thrown at them. The only setbacks and dangers they suffered were Komori not acting like a typical hamadryad, Ochako's surprise Bloodrage usage, and the boulder trap level.
  • Because of incredible synergies between Ashido's, Kaminari's, and Monoma's abilities, the dungeon group creates a battle plan that wipes out sixty-seven Cynocephalii despite their much smaller numbers.
• Dark and Troubled Past: Invoked by All for One. He manipulated the circumstances of Tomura's Quirk Awakening to destroy his home and family and leave Tomura wondering the streets until All for One "finds" him. Tomura did not realise the manipulation until Izuku points out that it is nigh-impossible for the authorities and society in general to randomly drop the ball that hard for him.
• Death Course: Izuku and Tomura (mostly the latter) makes the second-last level of their dungeon as lethal as they possibly could. The first version of it is a series of boulder traps directly and explicitly inspired by Sen's Fortress from Dark Souls I with several slime and projectile traps. It also habituates panicked invaders into running as fast as they can so that by the time they reach the last corridor, they'd be more likely to miss that the exit is in the middle. A later version adds even more projectile traps to harass invaders trying their damned best to survive the boulders by trying to jump back into the corridor they came from in the brief window between one boulder reaching its end and the next one starting. When asked for her opinion, Aeonia admits it's devious, and suggests ways on improving it.
• Death Is Cheap: When a Dungeon Servant dies, it's not that big a deal. The Dungeon can just revive them if they recover the souls fast enough and have the mana levels to spare.
  • Tomura to tell Himiko to die tactically so that the people after Ekana will assume Ekana's dead without further investigating.
  • Kirishima for his part is upset they have become jaded to their comrades dying due to how they'd soon see them again.
  • Dabi does a suicidal reckless charge that takes down several enemy witches. Tokage and Tomura are thinking of making it a more common tactic for him since it's one of the few times Dabi is worth putting up with.
• Deliberate Values Dissonance:
  • For a mortal, being told they will have a life sentence of forced labour is horrifying. For a daemon, it is a merely an inconveniece.
  • The Twenty-Six Tribes' opinion on slavery is very different from Izuku's. To the tribes, anyone able-bodied adult that doesn't contribute to the mutual defence of their people is a slave. However, slaves don't get mistreated or underfed as that compromises their ability to actually do labour. If a slave-owner kills a slave as punishment, it means they couldn't control them and everybody else laughs at them. Izuku however detests the very idea of slavery even if he can understand the pragmatism involved in how the Twenty-Six Tribes do it.
  • The Twenty-Six Tribes' don't treat relationship fidelity as seriously as Izuku does. Elder Anaya thinks Uzar is too faithful to his wife, and views it as unhealthy.
• Dem Bones: The Breathless Tide have a category of undead called Skeleton, which are just walking skeletons.
• Desperately Craves Affection: Izuku and Tomura quickly realize that if Himiko's feeling lazy, a quick way to get her off her ass and do some work is to tell her either Izuku and/or Ochako would appreciate the effort.
• Didn't See That Coming:
  • Anyone who visits Izuku's and Tomura's dungeon are caught off guard by them and their servants being more intelligent and creative than they should be for the number of levels the dungeon has.
  • Elder Anaya is caught off guard by Komori calmly deflecting her fire spell and counterattacking since hamadryads stronger than her usually panic at any sign of fire.
  • Elder Anaya's party are shocked when Ochako uses Bloodrage against them since the dungeon servants of a dungeon that's only six levels big should barely be sentient and not worthy of divine theurgies like Bloodrage.
• Didn't Think This Through: Himiko throws her torch at the hamadryad while fighting her. While it helps and she ultimately kills her opponent, it also started a small fire. Thankfully, it is put out before it could grow out of control.
• Disappeared Dad: Whoever Kirishima's and Tetsutetsu's father was, he's a complete deadbeat that left their respective moms to raise them on their own.
• Discard and Draw: Izuku and Tomura have the ability to switch skills around for their subordinates. They can't do this freely though as the more skills they have, the higher the mana they need to function.
• Distracted by My Own Sexy: Himiko is briefly distracted by the fact Tomura made her breasts bigger when she takes off her clothes.
• Drama-Preserving Handicap:
  • If mana-levels allow it, a dungeon can freely change the layout of a floor, unless there are outside forces present. This means no making new traps for active hostiles to make things easier.
  • A dungeon can make a lot of things, but it can't spawn ready-to-be-eaten food just like that. Izuku and Tomura don't know why they can't but it forces them to put in more effort to properly feed their servants. Luna later clarifies that it's an intentional limit put in place by the High Gods.
  • A dungeon has a lot of control over their servants, but there are limits. They can't force a servant to speak, and Izuku extrapolates they just can't force indentured servants to tell them things.
  • If a dungeon tries to cheat logistics by spawning servants with equipment in hand ready to fight, it'll raise their level and cost more mana. If however they instead take the time to craft the equipment separately, it will not raise their level and the mana costs will be lower.
• Dude, Not Funny!: Izuku tries to make fun of Shigaraki having opinions about meeting allies in sketchy places only to learn that's how Magne died and apologizes for it.
• Dungeon-Based Economy: It is possible for societies to make deals with intelligent enough dungeons for the society to obtain goods from the dungeon in exchange for the dungeon taking the occasional casualty and new goods to produce. This doesn't unbalance the economy though since more valuable goods require higher mana levels to produce, which necessitates braving more dangers to get them.
• A Dungeon Is You: Izuku and Tomura are made the joint consciousness of a dungeon's core, and have to work together to get things done.
• Easy Logistics: By using Laws, Izuku and Tomura manage to simplify the food logistics for the daemons and creatures by making it so that animals they can feed on regularly spawn.
• Eating the Eye Candy: Himiko isn't shy about appreciating Ochako's look both in general and when she's in action. Izuku sometimes joins Himiko in appreciating Ochako.
• Enemy Mine:
  • Enforced. The hero students and the League of Villains are forced by Luna to work together to survive. Especially Izuku and Tomura since as the joint consciousness of the Astral Core, anything they do with the dungeon requires them both to agree.
  • The threat of the Pentagram is the sort of thing that gets people who would normally fight each other to team up to deal with it.
• Energy Economy: The tokens issued by a Dungeon to use as currency are mana-bearing crystals that gets filled by the Dungeon. The risk of inflation with such a currency is minimal since the mana is a consumable power-source.
• "Eureka!" Moment: Izuku realizes they don't have to make creatures fit the edge of the level limit for a floor, they only need to make sure there is a clear difficulty curve. This gives them a lot more creative freedom in designing levels.
• Eviler than Thou: Luna tells Tomura straight up that by the standards of the new world, he'd be a mild annoyance at best, since the really evil groups cross further lines than he does.
• Evil Versus Evil: The Purifier loves it when two evil factions fight each other, since whatever the outcome, the totality of evil becomes weakened from their fighting.
• Fan Disservice: Whenever Izuku feels Tomura went too far, he gets payback by showing him images of naked All for One and Dabi. Worse, they are shown as catboys. Izuku also uses other men in his torment of Tomura.
• Fantastic Drug: The honey of the Blood Hornets can be processed into potent aphrodisiacs.
• Fantastic Firearms: After analyzing the rifle they found, Momo realizes it operates of magic, not gunpowder.
• Fantastic Legal Weirdness: In the original world Izuku and Tomura came from, there is the Dogman Precedent. The incident involved a feral dog with a Quirk that allows it to transform. It transformed into a human. All attempts to reason with it failed, and so the authorities ruled it is only an animal and put it down like other dangerous animals.
• Fantastic Slur: 'Low Elf' is almost a derogatory term for elf hybrids in general.
• Fictional Currency: Dungeons tend to issue tokens that are used as a currency in a community they oversee.
• Full-Frontal Assault: Ochako and Setsuna noticed that several beast-kin went into battle naked, and quickly discover why when they use Bloodrage, which is more effective the more of their bodies gets in contact with the sacred blood provided by one of their gods.
• Gaslighting: Dabi accuses Shoto of trying to gaslight him into thinking he isn't Touya, only for Shoto to say gaslighting doesn't exist.
• Gender Is No Object: Izuku and Tomura notes that among the Beast-kin they are dealing with, gender doesn't seem to be an issue among them.
• Girl-on-Girl is Hot: Denki's first reaction to seeing Ochako kiss Himiko is not shock that the former is kissing her enemy, but delight.
• God of Evil: Luna outright calls herself a god of evil, and between her domain of anarchy and her actions of dumping people into a life-and-death situation in Chapter 1, she lives up to her claim.
• Going Native: Izuku is worried that he and his companions are adapting too quickly to the new world, from Ochako converting to the faith of one of the local gods to the hero students adapting their morality to the lower standards for good.
• Good News, Bad News: Tomura tells Izuku the good news that the latter's slime trap worked, before giving the bad news that the intended non-lethality feature didn't work properly and Itar, the person who fell for it, is dead.
• Grave Robbing: The High God Mors detests grave robbing and his spirits the Gravehounds are created specifically to deal with grave robbers.
• #HashtagForLaughs: When Yla gets particularly annoying, Tomura says "#YlaIsABitch".
• Healing Checkpoint: Node Rooms contain secondary dungeon cores that allows skilled enough mages to tap into the mana flow of the dungeon, allowing them to use the dungeon's own mana to cast spells.
• Healing Factor: Trolls can regenerate from most injuries quickly.
• The Heart: Tomura reflects that something that the League of Villains sorely lacked was someone who could bind the team together and teamwork and camaraderie.
• The Hedonist: Rapturous Ecstasy as a pantheon cares more about their short-term gratification than any serious long-term plan for domination. When fighting a war, they don't actually care about winning. Losing is just another experience for them.
• Hidden Depths: Izuku is shocked to learn Tomura knows the entire criminal code of Japan.
• Hoist by His Own Petard: It doesn't come to fruition, but Tomura admits to Izuku he was already considering killing All for One for being annoying. On further prompting, he also tells Izuku that All for One taught him to destroy everything he finds annoying and says his mentor shouldn't be surprised by that, which Izuku concedes to.
• Househusband: Kaminari is open to being a househusband if it means getting a harem of women who'd dote on him.
• How They Treat the Help: Tomura advices Dabi to be nice to the help, citing that people like cooks and cleaners have easy ways of inflicting karma on the people who mistreat them. He mentions he insulted Kurogiri once over leaving his room a mess, and the latter retaliated by teleporting insects into his room.
• I Have Your Wife: Luna forces Izuku to comply with her orders to kill the chosen of her sister by threatening eternal torment of his loved ones.
• I Know Mortal Kombat: Amazingly, and quite inexplicably In-Universe, Spinner knows a lot of useful skills, ranging from driving to handling money to equipment repairs and maintenance, from playing video games. One of these skills is making earthenware out of clay, which comes in handy in making efficient golem bodies for the Earth Elementals.
• I'm a Humanitarian: Cynocephalus are a type of daemon based entirely on the concept of eating, and engages in cannibalism.
• Indy Escape: The boulder level is a multi-sequential series of boulders chasing intruders down straight and narrow corridors. After Tomura shows it to Izuku, the latter calls it materialized murder. Tomura mentions he was inspired Dark Souls I, specifically Sen's Fortress.
• Inexplicable Treasure Chests: Justified. Izuku and Tomura use the Laws function to place treasure chests containing loot that refreshes at set intervals.
• Infodump:
  • The fox-beastkin elder tells her companion Uzar a lot about what she heard about how dungeons work in Chapter 7. This is useful for Izuku and Tomura since they manage to hear the entire explanation and put up a convincing act to outsiders.
  • Aeonia gives a long explanation on the cosmology and theology of the world in Chapter 17.
  • Chapter 20 provides descriptions for several different spells.
  • Luna explains how the Laws mechanic work for Dungeons in Chapter 20.
  • Aeonia explains the magic system and its subcategories in Chapter 30.
  • Chapter 47 begins with the Dungeon Group learning a lot of things about the region from Lorae.
  • A big portion of Chapter 94 is dedicated to the ancient history of the world starting from First Empire who ruled the world for ten thousand years, covers their one competitor, the Serkarkans, who created the Labyrinth, and what happened after First Empire collapsed, which includes several new empires like the Xylian Dominion rising from the ashes. As explained by Momo, the Xylians were the ones who created the dwarves, ogres, and elves. Momo also elaborates on the Xylian's downfall, which was them picking a fight with a seemingly small cult of machine worshippers who were far more powerful than they looked.
• Insistent Terminology:
  • When Tomura realizes them just taking things from the burial site they found counts as grave-robbing, Izuku insists on calling it "archeology". Momo eventually disabuses him of this notion. She says that for something to count as archeology, it has to be done for the purpose of advancing knowledge and items taken have to be placed in a museum or otherwise used in study. What they are doing is taking things for personal benefits.
  • Luna prefers calling it "kidnapping", not "isekai".
• Internal Reveal: In Chapter 29, Aeonia learns of Izuku's and Tomura's dungeon's uniqueness, and that Luna is responsible.
• Interrupted Intimacy: Izuku's and Ochako's kissing session gets interrupted by the first major invasion their dungeon has to deal with.
• It Only Works Once: Luna's failsafe to protect Izuku's and Tomura's Astral Core from certain doom is explicitly a one time thing only.
• It's Personal: Tomura's hatred of All for One becomes personal when Izuku makes him realise All for One manipulated the circumstances that led to his beloved pet dog Mon-chan dying.
• Klingon Promotion: It is perfectly acceptable among Amazons to move up the ranks by beating their superior in combat, even spontaneously.
• Laser-Guided Karma: Tomura makes damn well sure to punish Yla for her excessively abrasive attitude by making her hand over her gear and leave in nothing but her underwear.
• Leaning on the Fourth Wall: Denki once shocked himself while chewing on cables, which put him in one of his... moments where he claimed they were all living in a shounen manga.
• Leeroy Jenkins: One criticism Elder Anaya has of her own culture is the tendency for her people's youth to charge straight into a fight for glory, and dying due to the charge being poorly thought out.
• Let Me Get This Straight...: In Chapter 19, Yaoyorozu sums up the story premise and events thus far to see if she understands everything.
• Lock and Key Puzzle: For Floor Twelve of their dungeon, Izuku and Tomura, they use Laws to make it so Adventurers must acquire two keys from the Rapturous Ecstasy camps before they can unlock the stairs to the next floor.
• Love Makes You Crazy: Himiko is perfectly happy to die on Izuku's orders because she could get him to call her by her first name after she gets resurrected. Izuku lampshades this to Tomura who tells him he long stopped expecting logic from her.
• Magitek: The old Xylian Dominion had machines that were powered by magic, including a tank-mecha that was powered by a mana reactor.
• Manchild: Dungeons with only some levels are supposed to be immature at best. To keep people from realizing that they're an outlier, Izuku makes Tomura represent them when the beastkin tribe representatives meets with them.
• Masculine Girl, Feminine Boy: Izuku and Ochako develop this kind of relationship, with Ochako being the fierce warrior recognised by the local war god, and Izuku being the softie that's hers to protect.
• Meaningful Name: The dungeon group notices that the names of the High Gods are derived from Latin. Saevius for example is derived from the Latin word for 'cruel', 'barbarous' or 'savage'. Luna is a moon-based name and she is a moon goddess. Same with Sol the sun goddess.
• Mercy Lead: When Ochako learns that Tenya tried to kill Stain and that Izuku and Shouto were there from Himiko, Ochako gets upset about not being informed and gives Izuku a ten-seconds headstart before she starts chasing him down over that grievance.
• Metaphorically True: Not wanting to outright lie to Himiko but also not wanting to alienate her, Izuku tells her that Ochako is thinking warm thoughts about her. Tomura is quick to clarify that it means Ochako hopes she burns in hell.
• Mind Rape: Trolls can eat minds (not brains, minds) with their eyes, leaving their victims as vegetables.
• Mission from God: Luna the goddess of anarchy and revolution orders Izuku and Tomura to kill the chosen of her sister, after which she will leave them alone. Izuku has reservations due to Luna being a self-proclaimed evil god.
• Morality Chain: Izuku and Ochako together becomes Himiko's moral restraint. If she is about to go too far, they will stop her.
• Mr. Exposition: Aeonia is the first being the dungeon crew encounters that they could ask things about the world, and she more than delivers with in-depth explanations.
• Mundane Luxury: Mr Compress manages to get the hero students to turn a blind eye to a blatant act of robbery by showing off one of the stolen goods, soap, something they were sorely missing in their isekai'd life.
• Names to Run Away from Really Fast: The trope is name-dropped when Tomura learns that one of the old names for Rampant Bloom is Locust-That-Walks. Izuku agrees with his sentiments.
• Necessary Drawback: Izuku and Tomura can't just give their subordinates as many abilities as possible. More skills requires more mana levels for their subordinates to function, so if they give too much, they can't do things outside of the dungeon so easily.
• New Life in Another World Bonus: Invoked. Luna read up more of the isekai genre and realizes she didn't give Izuku and Tomura special cheats isekai protagonists usually get, and so, gives them some in Chapter 20. Their bonuses are as follows:
  • They now have the ability to cash in divine favour for gifts from the various deities. This ranges from summoning shard spirits and daemons from their domains, to having one entire level modelled after a single spiritual world.
  • Izuku and Tomura are given additional flexibility in managing dungeon servants not available to other Dungeons. There are some limits for balancing reasons, but the options are as follows:
    • Normally, souls contracted to Dungeons can have skills inserted into them by the dungeon, but lose them when they leave. Luna makes it so that with Izuku and Tomura, they have the option of keeping those skills. However, they cannot rejoin the dungeon. The decision to leave will be permanent in that case.
    • The souls made up of the My Hero Academia characters also gain the ability for independent growth and give the dungeon access to new skills that way, but, they must decide on a permanent body. No body switching is allowed for any individual that makes this choice.
    • The souls made up of the My Hero Academia also have the option of overriding the soul of a daemon they captured as opposed to getting to agree to serve them. This choice is also a permanent one, and Luna is giddy to see the results of that.
• Nightmare Retardant: In-Universe. The more Izuku learns of and deals with the eccentricities of the League of Villains, the more their previously intimidating image gets broken.
• Non-Answer: When Anaya's group asks Tomura how he managed to get servants of Mors and servants of the Breathless Tide to co-exist on a single level when they have a large amount of animosity, he just answers that he's persuasive without going into details. When they don't buy it, he gives in and explains how he did it.
• Non-Human Humanoid Hybrid: Low elves are the product of elves breeding with either different elven species, or even non-elves. They're sterile, and almost always suffer from various birth defects. Most elves specifically avoid interbreeding to avoid giving birth to a low elf since with those issues, many of them consider it better to avoid being born.
• The Nose Knows: When Himiko pretends to be Ochako while Ochako pretends to be Himiko for a prank, Monoma immediately realises who is who because his beastkin sense of smell is sensitive enough to tell one of them is very horny, and that one could only be Himiko.
• Our Elves Are Different: Aeonia snorts at the notion that elves are peaceful nature lovers who happen to be good with magic and bows. She explains that in the past, they're actually quite martial, with several of their elites being bloodthirsty warriors. In the present, they realised that the bloodthirsty warrior-culture was a double-edged sword and reorganised their self-governance to emphasise martial might less when it comes to deciding who gets to rule.
• Pay Evil unto Evil: Followers of the Overtyrant believe in giving no quarters to the wicked. If they find an evil overlord, they'll torture and kill him and his supporters, cannibalize them, and tell they're previously oppressed citizens that if they follow in their footsteps, they're next. One redeeming factor is that the Overtyrant knows who's good and evil and if their followers try to use his magic on a good person, it won't work, or even backfire.
• The Peeping Tom: Himiko spies on Izuku and Ochako when they have sex for the first time.
• Pervert Revenge Mode: When Tomura shows Izuku a preview with an image of a naked Ochako, then alters it so her breasts becomes bigger, Izuku retaliates on Ochako's behalf by showing Tomura a naked Dabi.
• Pocket Dimension: Pass the first level of a Dungeon, each separate level is technically its own separate space. This allows Izuku and Tomura to move the passageway between levels on one floor without affecting other floors.
• Platonic Life-Partners: Discussed. Tomura thinks best friends of compatible orientations and genders are just couples in denials in defiance of this trope.
• Power Perversion Potential: When Himiko hears of Black Whip, she immediately blushes, making clear she is thinking of the sexual applications.
• Pragmatic Villainy: One veteran beast-kin warrior stops four rookies from raping a captured prisoner from the Rapturous Ecstasy forces not because he was morally opposed, but because the battle is still ongoing and they still have to finish it.
• Psychopomp: One of the local gods is Mors, the Exarch of Passage. They are the High God of death, funerals and mourning.
• Reality Warper: Once a Dungeon unlocks Laws, they functionally become able to warp reality within their domain in exchange for mana. The more they try to push against "narrative logic" as Izuku and Tomura understands it, the more mana it costs.
• Red Baron: Where hero names are largely abandoned, Komori gets a new one in Chapter 69 after she becomes an archdaemon, Mycelium Singer.
• Related in the Adaptation: In canon, Kirishima and Tetsutetsu are unrelated. Here, they are almost certainly half-brothers through their deadbeat dad.
• Relationship Upgrade:
  • Izuku, Ochako, and Himiko become an official triad in Chapter 36.
  • Setsuna confesses to Shouto and they become an item, which Izuku finds out about in Chapter 97.
• Rule of Three: In Chapter 19, thrice Tomura tries to rebuke Momo's assertion that the League of Villains have a poor track record, and thrice Izuku points out the issue with each argument he makes.
• Sarcastic Confession: When Lorae asks where they came from, Monoma answers they were heroes-in-training from a world without magic in such a way that Lorae doesn't believe him.
• Schizo Tech: Following their victory over the Ecstacy forces, Izuku and Tomura are astounded to find a gun in the loot they got where everything indicated they were in a medieval fantasy world.
• Screw This, I'm Outta Here: In Chapter 58, Anaya's party see the large swarm of Cynocephalii coming at them on the Dungeon's seventh level and immediately noped out of there.
• Sealed Evil in a Can:
  • Justified. Izuku realises that due to the afterlife being confirmable fact, and due to the fact that people from the afterlife can come back to the mortal world, killing powerful enough bad guys is not that good of a long-term solution. Sealing them away instead achieves longer lasting results than just killing them would.
  • Taera the Spiderkissed is a powerful tenth-circle witch of the Rampant Bloom, and due to the danger she posed, she was sealed away. The Webmistress Family are trying to free her.
• Secret Art: This is what separates the rank-and-file combatants from the elites. Most people have easy access to the manuals for basic techniques, but only the elites have access to the manuals that teach the advanced and incredible techniques.
• Seeing Through Another's Eyes: Dungeons have the ability to see through the eyes of their servants, as well as more generally experience the world through their other senses.
• Selective Obliviousness: One huge blind spot for Izuku is him giving Bakugou undeserved admiration. Even Tomura can see Bakugou's flaws, but Izuku refuses to see them.
• Shameful Strip: Because Yla was so annoying that even Izuku was brought to the limits of his patience, Tomura demands as part of their deal with the beastkin tribe courting them that Yla hands over her gear. Anaya and Uzar, also equally done with her, leap at the chance to ruin her day and she ends up having to get back out of the dungeon and back to their tribe in nothing but her underwear.
• Shameless Fanservice Girl: Himiko has zero qualms about using her body to get a reaction out of Izuku.
• She Is Not My Girlfriend: Izuku denies Ochako and Himiko are his girlfriends to Tomura in Chapter 16. Tomura just grumbles at him.
• Shipper on Deck: Shouto ships his mother Rei with Izuku's mother Inko, then quickly adds All Might to the mix.
• Shout-Out:
  • Tomura references Dark Souls I, specifically the Sen's Fortress location, as the inspiration for his boulder trap level.
  • When Yaoyorozu and Kirishima first manifest, they point to each other in a way that reminds Tomura of the famous Spider Man meme.
  • Apparently, Compress loves dressing in the creepiest clown outfits available and scaring the crap out of random people by disappearing when a vehicle breaks their line of sight, like Pennywise from It.
  • Tomura namedrops Monster Musume in Chapter 88.
• Simple-Minded Wisdom: After they realise that Izuku is functionally immortal if no one manages to kill him, he and Ochako angst over how that could impact on his relationship with her and Himiko. Himiko tells them they are being dummies worrying over something that would only become an issue in a hundred years or so, more than a lifetime away, and they don't have to let it affect them now. Izuku and Ochako admit she's right.
• Skewed Priorities: Tomura is more concerned with the reveal that All for One manipulated him into killing his pet dog instead of the reveal he manipulated him into killing the rest of his family. Izuku calls him out on this, but Tomura justifies himself by making the compelling case that his dad was abusive and that the rest of the family did absolutely nothing to help.
• Slave Liberation: The slavery system of the Twenty-Six Tribes have two separate built-in methods for a slave to free themselves. One is the Trials of Freedom. A slave can issue a combat challenge for their freedom, and if they triumph, they are freed. The other method is for them to flee and if they can escape pursuit for three days, they are declared free.
• Snake Oil Salesman: The Webmistress Family likes to send some of their members to pose as normal herbalists. These herbalists would then render various women barren, which makes them more susceptible to the recruitment pitch of the cult. When the Purifier tells her allies this, Ochako and the rest are infuriated by what the cult does.
• The Social Darwinist: The goddess Occasa does not mind that much that Izuku's and Tomura's dungeon killed some of her cultists, because their victory proves her servants were weak and therefore deserved to die.
• There Is No Kill Like Overkill: The long-defunct Xylian Dominian had a riot-dispersal machine that happens to be a tank-mecha. Tomura lampshades the overkill and Aeonia just explains the Xylian Dominian liked to "disperse riots straight into the underworld".
• Superhuman Trafficking: The Astral Core of a dungeon is extremely valuable, but the only ethical source of it is from authorized executions of homicidal ones. Demand far outstrips the legal supply and dungeons that don't deserve that fate may find themselves facing people trying to kill them and take their core.
• Stalker with a Crush: Ochako succeeds in getting Himiko to downplay this trope by making her understand that respecting boundaries will endear her to Ochako and Izuku better than her simply violating their privacy and personal space.
• Taught by Experience:
  • Izuku and Tomura are tossed into the deep end by Luna with minimal aide and guidance in fulfilling the task she gave them, and so have to learn almost everything about how the dungeon and the world in general works through experimentation and experience.
  • The fox-beastkin elder admits that she used to be a rash youth alongside the rest of her generation. And then she noticed her fellows dying and learned better, becoming a wiser elder.
• Teeth-Clenched Teamwork: Izuku and Tomura don't like each other, but have no choice but to work together to survive. They do choose to get on each other's nerves though.
• Teen Rebellion: Apparently, the entire reason Ibara is a Christian is because she is rebelling against her parents, who are fashion designers who have a whole brand about making costumes like Midnight's.
• That Came Out Wrong: Kirishima is quick to point out the issue with Ashido's wording of calling Ochako and Himiko making out "unholy" since it comes off as homophobic without context when her actual issue is that her shipping chart is messed up.
• Their First Time: Izuku and Ochako have sex for the first time in Chapter 27.
• Time Dissonance: Lampades treat centuries and decades the way normal humans treat years and months. Izuku realizes that this is normal for those who have eternity and extrapolates it applies to all other daemons and higher-tier beings.
• Took a Level in Badass: In chapter 69, Komori ascends into becoming an archdaemon.
• Too Kinky to Torture:
  • To Ochako's consternation, her ability to punish Himiko for various things is severely compromised by the fact that Himiko enjoys being punished by her. Admittedly, an inability to permanently die takes most of the fear out of such things.
  • One faction of Rapturous Ecstasy daemons take this to the extreme. They get off on anything, like being eaten alive, or being raped. One of them is even disappointed the rape attempt on her is interrupted.
• Total Party Kill: The Webmistress' Family forces sent against Izuku's and Tomura's dungeon suffer a total wipeout.
• Trapped in Another World: From the perspective of the characters, they were forcibly taken from their world and have no hope of ever going back.
• A Truce While We Gawk: While the Dungeon fights the Webmistress Family, Ochako and the spiders stare in shock when a dragon suddenly lands in the middle of the battlefield.
• Underestimating Badassery: The Webmistress' Family forces that went after Izuku's and Tomura's dungeon grossly underestimated their threat level, though to be fair, they had no reason to believe the dungeon was more dangerous than it should have been for its relatively small size as they had no way of knowing the divine intervention involved.
• Un-person: One of the outcomes of the Black Iron War is that details on who the Xyls were being wiped out due to the cult they foolishly picked a fight with unleashing a conceptual bomb that wiped out all memory of who they were, affecting even physical records.
• Weirdness Magnet: In the one week Spinner and Lenka explored the lands neighbouring the Dungeon, they encounter a swamp with a hydra in it, a cave system with a drake in it, a troll (which in the setting, are very dangerous creatures), an opium plantation, meet naiads, and find an active gold mining operation run by moon elves, servants of Luna.
  Lenka: I’ve seen more crazy and awesome things in the last week than I’ve seen in my whole life!
• Wham Episode: In Chapter 91, the Dungeon gains a servant they could ask for up-to-date information on their surroundings. A cat-girl Spinner met named Lenka.
• Why Didn't I Think of That?: Izuku calls out Tomura for his stupidity as a supervillain leader by pointing out that since Himiko was able to turn into him, they had the perfect way to frame him of serious crimes and ruin Izuku's hero career. Tomura for his part is shocked he himself did not think of such a brilliant plan.
• Wild Card: Luna thrives on being chaotic and unpredictable, even in how she helps or be a jerk to Izuku and Tomura, even while they have to kill one of her sister's chosen ones for her.