There's lots of room for polish.
I can't pinpoint what makes me think this, but something (or three?) feels off about the story. I couldn't enjoy it.
The balance... Well.
TLDR:
Please allow the player to have more strengths to make use of. Either that, or have the enemy's attacks match better the limited strengths of the player character.
Full version:
I didn't have fun due to the unfairness of the enemies. Utsuho fires these fast, ondulating, random bullets frequently, and the player has nothing to compensate. We got a big hitbox, we move slow so no getting out of the way quick, no other way to shoot at the boss than being at the same height (which is the aforementioned zone of death), and no mercy invincibility.
In other words, there's no way to do skill-based gameplay.
Boss!Sagume is barely more tolerable. Has the same problems but not on the same intensity for each. The curving bullets are actually okay somewhat. But the high speed random salvos... at times you just cannot dodge, end of story.