Hey. This is sick as hell. Delightful stuff. The moon's face at the end was a very good bit. I also smile at the choice to include a Game Boy filter in the graphics options, as building a fighting game-type experience in Usagi feels very much of the same spirit of those ambitious FG ports on the Game Boy and Game Gear.
If there's anything at all I found I struggled with, it might be that the back end of the hitboxes for Usa's attacks, particularly the jump kick, are a hair less forgiving than I would expect, leading many opponents to slip past me. Easing up on that, however, might eliminate the challenge, so I'm not committed to calling it an issue.
Anyway, great work. Really enjoyed my time with it.