Quite fun! And it was funny! I liked that a lot.
It reminds me of Touhou 17.5, in that it's an attempt at bringing Touhou-esque boss fights into a 2D action game. But instead of your attacks/dash being able to destroy bullets, you can freeze them and then platform on them or break them. It's a fun twist.
The final phase got a laugh out of me when I realized what I was supposed to do lol
Unfortunately, I didn't really "figure it out," and more-so just did Perfect Freeze because nothing was happening, and then I realized "oh, she literally just hit her face and fell." I was expecting a "cooldown" period during the attack since the previous phase worked like that.
To echo some previous comments, the controls felt odd to get used to. If I had to pick a reason as to why, I'd say it's because the jump and attack buttons are separated by another action button. This is pretty atypical. We're pretty conditioned to assume that, in a 2D game like this, "jump" and "primary other action besides jump" are mapped to buttons that are next to each other. Like Mario (jump and run/use Powerup) or Castlevania (jump and attack).
There's some fine-tuning that can be done which was most likely thought about, but game jam time limit and what not. Such as attacking having a hit sound effect. Which would've helped attacking feel more "satisfying" (I can't think of a better word). The animation for it was good though, which is a large part of making an action feel satisfying to do.
Also, the portraits were very good and funny and I love them and Advent Cirno.
I also like the inexplicable lore that Cirno knows what Detroit is.
Good job!