Very interesting concept, despite the fact that it's not really connected to  the"protect" theme. I love the art style and the overall "demon" theme but it feels quite out of place with the mechanic itself, it's also a real shame that given such cool sprites the player has to focus only on the part of the screen with the numbers; I would have put the equations over the demons personally, it would have been more impactful. Anyway, great job!