Adding bullet hell-ness to a platformer kind of necessitates the addition of some other ability. Effectively making Kirby's float into a faster, hold-able version is an interesting choice to incorporate added mobility that makes it easier to move around bullets. (More like Kirby 64 in which Kirby can't hover forever, and he'll eventually start falling.) Though I can't help that I missed the "oomph," or rather the strong feedback, that a more typical jump does, if that makes sense. Partly because it doesn't make a sound, but I'd say the larger part is because there isn't that initial strong force that lifts you quickly off the ground. The velocity is seemingly consistent the entire time you rise, but this does have the benefits of also making it more consistent for doing what it's intended to do, which is help you move around bullets.
This did also make bullets which were closer to the ground more threatening since you can't get out of the way as quickly as you could with a normal jump, which I thought was a novel problem to have to come to grips with over the course of the game.
Especially noticeable with the boss was that I wasn't sure if I was hitting something or not since your attack doesn't make a sound upon impact. You'd want such a sound to be pretty subtle, though, like it is in Touhou, but noticeable enough that you know you're doing damage. Feedback like that is really important.
The sprites were very cute, especially Marisa! I love her expressions.
I thought it was a fun game all around. Good job!