I really liked the character art and the whole opening cutscene sequence! I really liked the look of the characters, especially the smirk on the bad guy's face. I think it shows his personality very well.
Gameplay-wise, I can definitely see similarities to Punch-Out!!! There's a lot of potential to these mechanics, for sure, so I think you can grow what you have now into a very fun game!
I have a couple notes feedback about how it's working right now; I also saw your note that you had a bigger plans, though, so my ideas might already be a bit out-of-date.
- Player / enemy attack windup: In this kind of game, I think I'd prefer my character's attacks to be very quick and responsive. No (or almost no) windup (making the attack hit the enemy in less than a 10th of a second, or something) would make my character feel responsive and make it easy to react to what my opponent's doing.
On the other hand, I'd like the enemy to have more windup. The enemy does change stance when preparing for a low swing, but the high swing hits immediately. In a punch-out style game, I'll probably be watching the enemy 90% or more. Figuring out how they broadcast their attacks (maybe with a big animation, maybe with something subtle) is a lot of the fun. Making the animation isn't easy, though, so I definitely understand the time limit in the jam could've limited what you wanted to do. - Player idle animation: Since my attention should probably be on the opponent most of the time (watching for tells, getting ready to dodge and counter-attack) I think I'd probably prefer having the player character have a calmer or more subtle idle animation. Art is not my area of expertise, so I could be totally wrong about this, but my instinct is that we probably want the bad guy's movements to be the most eye-catching thing by default.
I can imagine this might also be part of the game jam constraints, your plans for the enemy's animation might have also been more expansive.
I could also see the player character's bobbing animation being really good if it matched the beat of some kind of background song - then it might help get me a better sense of timing or something cool like that.
Overall, nice work on your game! Getting the whole thing together with starting menus, a cutscene, and gameplay is not an easy thing. I'm interested to see how your ideas develop in future versions.