I like the idea of the mechanic, but I wish the sprite in the middle stood out a little more - I played against Yuki and didn't notice it right away until it's expression changed, so for a second I didn't realize hitting L was actually doing anything. I think adding a few animations of the player characters moving/casting and maybe some audio feedback would really help get that message across though!
I also don't really know if I understand what's happening in the art. At first I thought it was in a church, but also there's wizards and a prisoner and some sort of sprite demon, and it feels a little bit disjointed. I do think the spell books and the starburst effect make it really clear that you are meant to button mash, though, nicely done!