making Yin look more cartoon-ish as an actual character design for the app/game ( pretty excited about this! ) the first thought i had as a viewer "hey don't ya judge me black demon!" D: used paint tool sai and photoshop.
This kinda reminded me of Scourge if you ever read the Warriors series. He's this black cat that becomes a demonic like cat after being deemed weak most of his life until he decides to show his ability to kill.