This plugin will let your unity import .piskel files without exporting it.

• Import .piskel file without exporting it
• Importing Every frame and Every Layers

• Using unity version must be higher than 2020.3x
  looks like its still supports 2017.1 but when using older than 2020.3x you must import Newtonsoft.Json
• Cant merge all Layer

You can use the plugin with importing the latest(or previous one if needed) release on your unity project.
just right click on the project window and go Import Package > Custom Package... and select the downloaded unitypackage file.