This is a really cool project! I love when bullet hell is used not just as a mechanic but also as an aesthetic piece, and this game does an excellent job at that–visually beautiful and great music too. The patterns are also fairly creative and pressure you in neat ways.
I do have some gripes, but they involve the later parts of the fight so I’m going to attempt to spoiler tag it here. (I haven’t used the spoiler markdown on here before, so I’m hoping it formats correctly?)
Boss spoilers
I feel like the healing mechanic has a negative effect on the pacing of the first two phases. The time between turns takes so long that you can spend several minutes trying to heal yourself back up only for all that work to be undone by just a couple hits. I beat phase 2 on my second try but the successful attempt was almost 15 minutes long which is pretty extreme--there's just not enough pattern variety to make the same attempt interesting for that amount of time. I'm not totally sure what the answer would be but if I were to play this again I imagine I'd have a better experience by just ignoring the healing entirely and cutting my losses when I get hit.The last phase is extremely difficult (it accounted for 106 of my 108 deaths!) which I’m not inherently against, I love a solid bullet hell challenge, but the time it takes to get back into another attempt adds up incredibly quick and makes doing retries fatiguing. From the moment you run out of HP to being able to reset and get to the first pattern again, that’s over 20 seconds of downtime. Also, it’s possible that I may have missed a cue in the heat of the action, but the reversing bullets section at the end feels quite mean; there’s already some pretty tight jumps involved, so having to also memorize when to pre-emptively respond to an extra attack from off-camera feels overkill to me. Again, not sure if there was a telegraph I missed that makes it clearer when the bullets start reversing. You can kind of tell by looking behind the boss, but it’s still dicey.
Overall I had a fun time playing this.