This was a challenging game! I think the bosses had a nice difficulty curve overall for me, but I think the curves of their individual phases might have been a little rougher - on the final fight I took a lot more damage early on than I did later in the fight (although maybe I was just performing well under pressure). The patterns felt like they had a nice flow, and it was pretty clear how I was supposed to navigate them, if not on the first try, then on the first two or three rotations.
I'm not super familiar with the genre, so I think it might be helpful to have a mini-crash course for people like me. By chance I was aware of the star representing the hitbox, but I thought the focus button was going to make my bullet spread tighter rather than make me move slower. I also didn't think to hold it down since I just pressed it to play the game.
There also might have been a bit of a bug? I got stuck on a screen that said BONUS when I tried turning off the music after I beat the game. Which is to say I was just testing things out, not that I didn't like the music - I thought the music was very fitting and really enjoyed listening to it.