Oh this is cool! The math gameplay was pretty cool, although I eventually ended up just looking at the answers for the largest number instead of actually looking at any of the equations... still, the whole aesthetic/music/atmostphere is super cohesive.
The opening cutscenes were kind of long and a bit overwhelming -- I ended up paying better attention whenever you had a story beat during a gameplay segment. I think it helped that the number of characters I was introduced to was reduced, and the stakes (purify the enemies/save the little brother's spirit/etc etc) were directly tied in with what I was doing. After that it was easier to get into the story.
I also wish the text box background was a bit darker, or more opaque. Since it's translucent, sometimes the contrast between the white text and some of the lighter parts of the background were hard to read.
But overall, well done! I love it when UI elements are all crafted to fit one cohesive aesthetic. I also love all the character designs!