Incredible pixel art, fun and bouncy chiptune music. The music and the saturated palette remind me of the better GBA games, in the best way possible. This feels like it could have been an unreleased KogaNue platformer for that handheld. Nice work with the tree animations (I guess that was a shader?).
Moving and attacking feels pretty good. I have tried to make platformers before, but I always struggle with making the movement feel good; you must have put a lot of work into it. Only after beating the game and reading the comments did I realize that I could air dash, but things went fine without it. Lack of checkpoints and healing items hurt a bit, but it was manageable. I too was surprised that the fans hurt Kogasa. I think you were only missing a sound effect for when Kogasa was hit, but other than that the sound effects were all good. Reactive dialogue was a nice touch.
I would love to see this explored further with tighter level design and more enemy variety, but as it is right now, great job.