I played the initial version, so some of the points here might have already been addressed.
The intro is way, way too long, especially for a jam game. There's too much text and the scroll speed is too slow. There is a way to speed it up by holding spacebar, but I didn't know about that ahead of time and was afraid to push buttons lest I skip the intro entirely. I'd prefer if the backstory was presented differently, like in cutscenes, but time was probably a constraint here.
The story itself was pretty cliched and generic. As an excuse plot for a boss rush it's no big deal. If the game was longer or more story-driven I'd come down harder on it. Depending on where you plan to take this in the future that may or may be something you'll want to address.
I only played one set of battles, but it was pretty fun. It's mostly stock assets (with some custom scripts?) but the effects are pretty, the animations are fluid, and the sound effects have plenty of impact. It had some challenge, but wasn't super difficult. The battles were definitely on the long side, but they didn't get frustrating or repetitive. Both of those things may change in later battles, but I can only comment on what I actually played.
I found myself overwhelmed at the overall complexity. I never even understood what the icons for elements or attack types meant, I had no idea what the default attacks did until I tried them, I still have no idea which element is weak to which, I only discovered what "Lore" meant in the last battle and I never developed a good grasp on which character was good for what. I think in a full game where mechanics and powers are introduced more gradually, this wouldn't be a problem (or at least not as much of a problem) but as it stands the game just throws way too much at you at once.
Part of this is on me for not even looking at the character tutorials. I'm not sure if there's a manual, but if there is, I didn't read that, either. I can't speak for everyone, but for me, learning a whole bunch of complex systems is a bridge too far for a jam game.
I also found it weird that limit break is in the same category as the normal attack. Reading the changelogs, I think that's addressed in a later version?
Overall, I think the core of this game is good. There's lots of complex RPG mechanics that seem to work pretty well, and though the art is mostly stock it works well. The one thing that's sorely missing is progression; it needs to start off a lot simpler and perhaps a bit easier before gradually introducing complex mechanics that the player needs to master to finish the final battles.