The first time I played I found it very hard to shoot anything, I was expecting hitscan bullets but when I realised they were actual objects in the world, and with considerable drop at that, I found things very frustrating because it was basically impossible to hit any fairies with all of their bullets swarming me. That being said, I really liked the idea, and the movement felt good, weaving around bullets actually works surprisingly well, so I gave it another shot...
On my second playthough, I was able to appreciate the game a lot more. I took a methodical approach to attack the castle, making sure to clear all the enemies in each room before progressing so that their bullets did not become overwhelming. I got used to how to aim my bullets, and I also got to explore the castle much more, discovering alternate routes and even some secret passages (and a secret fumo) which is pretty neat! Taking a methodical approach was much more satisfying, especially when I managed to hit fairies with little effort.
I had fun, however, there are still plenty of areas I think could be better:
-Firstly, I was never able to get used to shooting the first time because there is little time/space to figure things out and fairies kind of just come and start attacking you. If you get overwhelmed at the start and fail to hit things, the whole game basically becomes unplayable. The beginning area should definitely be changed so that players aren't under pressure and can practice just moving around and shooting things.
-Although I did get used to the projectile bullets, and you could keep them like that if you're going for a certain game feel, I also think hitscan would feel nice and make it easier to hit things by quick reaction.
-I found certain cases where enemy bullets were passing through walls.
-Also, do the enemy bullets ever despawn over time? I do feel like the bullet number can just get ridiculous sometimes, especially if you fail to take out all enemies.
-As for the Doremy boss fight, the first phase was actually great! Second phase was worse though, and last phase is horrible. The thing that made the first phase so good was that dodging her bullets was feasable, but you can't really do that for the others, and for the last phase in particular, if you try running anywhere you get hit by loads of bullets and your HP is just melted super fast, so the best thing to do is just stand still next to a wall and try to shoot her down before you die.
I hope you found this feedback helpful, I really like the idea and what's there has elements that feel very good!