Its awesome to hear that you are loving the game. Never played Ultrakill but if you want to continue the shooting aspect then maybe you can spawn "numbers" on the map which players can pick up as an input for answers. Maybe this will help UX a bit. Hard to tell. I'm sure you'll figure out something :D
Viewing post in Math and Guns Jam Version jam comments
I have considered having the player pick up numbers, or maybe even making it so that you have to hit targets which have numbers connected to them, but I feel like things like that are done too much. I had also considered making the game more RPG like and having a turn based battle system, but another game does that, it's called Prodigy, and a part of the reason I am making this game is to fix the flaws in its design. In prodigy, because players have an infinite amount of time to do a math problem, most of them just cheat and look up the answers instead of putting in the effort to solve it. I want my game to have players not wanting to have to go and cheat to find the answers but rather for them to just do it with a pen or paper, or better yet, do it in their head. I also want the game to eventually be compatible with flashcards so I have to design partially around that too.