Mysterious Waif-tan is one of Trope-tan's many younger(?) sisters. She is the Anthropomorphic Personification of the Mysterious Waif trope.

Among her many mysterious qualities:

Enigmatic half smile.
Straight, almost narrow, ambitious-looking lavender eyes.
Waist-length cyan hair.
A slightly translucent, knee-length white dress.
May or may not be Really 700 Years Old. Seriously, she won't tell us.
May or may not know Waif-Fu.
Thought by some to be a Waif Prophet, but to others she seems to simply be a Deadpan Snarker.
Sometimes seen wearing a cross made out of raven feathers. Other times, she is seen wearing a golden signet ring embossed with a raven on a platinum chain around her neck.
Sometimes seen with the Chinese pictogram for tea tattooed upon her forehead.
Once reported to be seen taking on the form of a raven.
So mysterious that all attempts to picture her are doomed to failure. You are free to try, however.
It's strongly suspected that she is, in fact, the Database, captured in the body of a young girl.
Unconfirmed rumors hint at a rivalry between herself and Black Magician Girl-tan.
Fills in for Trope-tan's Five Things Band (under the TV Tropes folder) as The Heart.