Aseprite auto import (drag and drop files) plugin for Unity.
Just add https://github.com/renandresch/unityasepriteimporter#upm to your package manager (add package from git url) and wait a little bit!
Can import merged file atlas + sliced sprites + animations (by tag)
Supports layer merging (normal blending).
Supports RGBA, Grayscale and Indexed formats!
Can also import separate layers as separate textures + sprites + animations