I think I beat it? The game just cut to a black screen with the boss sprite in red in the corner. Regardless you did a great job with the art style, it really stands out. I don't know if I've ever really seen a mechanic like how you did the summon bar, that's a pretty creative way to give the player multiple summons without needing extra controls/menuing.
Once you get the summons that's kind of all you'll need to use though, your normal attack is just too short to risk using. I wish there was a bit more strategy to the combat other than just spamming bugs at the enemies.