I really like the atmosphere of this game! It almost felt like I was in a dream, and the background music complemented the visuals quite nicely. I am a sucker for retro graphics in games lol.
Oh and congrats on your first game jam! The first one is always the hardest, but I think you did a great job designing the atmosphere of the game. Sure, the gameplay is a little limited, but I find that the visuals, atmosphere, and sound design make up for it. This almost feels like interactive art.
The biggest feedback would be to make it more clear what the player is supposed to do. I know you put a detailed explanation in the game description, but in my experience people don't read those. It's better to put concise instructions right in the middle of the game. Like if in the beginning you put an epigraph like "HEMOPHONY —The sound of blood" it'd really set the mood. Then the instrument select screen should have a longer timer, maybe 15 seconds, because instead of reading the quotes that were on screen I was frantically trying to choose what instrument I wanted.
All in all, this is a great first game jam entry (much better than my first jam, that's for sure!). Great vibes, and great music.