This is a work in progress (though almost functionally complete) custom plugin for the Python Library Pillow that enables the decoding of files compressed by the ETC (Ericsson Texture Compression) algorithm. It is able to decode ETC compressed files from passed byte data, as well as from .pkm files.
In conjunction with UnityPack, this can be used to extract various assets from an Android Unity game, e.g. Shadowverse.
As of now, it can decode RGB and RGBA textures encoded with ETC1 and ETC2. It cannot decode R , RG, sRGB, or sRGBA textures.
Just copy this script into your project and import it, then use Pillow as normal.