Great-feeling shmup! I think I reached a kill screen after about 5 and a half minutes though lol - if you get rainbow bullets and upgrade past that it crashes the game, it looks like.
I really like the onion attack vs the asteroid attack forcing you to deal with them differently, it creates a great dynamic even very early on. Though, I think momentum is super important, since killing enemies early on and getting as many attack upgrades as possible is really what lets you stay ahead of the curve. At a certain point, the difficulty levels off since your attack power is high enough to almost instantly shred anything onscreen, and once you're shredding all those enemies, you get enough shield and health upgrades to not need to worry about taking damage nearly as much either. Oh, and at that point, the sound effects get a little overwhelming and crunchy as so many damage sounds stack up on top of one another at the same tiem.
Good patterns, hitboxes felt very fair, definitely hit that flow state! The music also fits the vibe great and helps ease into the flow effectively for me.