They literally are sprites from Fatal Fury: First Contact on the NeoGeo Pocket! :)
I'm using Kim as a placeholder character to help develop the engine!
Oooh, good choice! It fits the Playdate's aesthetic very well, and I hope something similar can be managed when you make your original sprites. Good luck with the engine, and making everything else! This game looks like it has potential, and I'm very excited to see what it looks like as a finished product :)