Great game, very impressed it was  made in 48 hours! The pixel art aesthetic is fairly simple but it fits the mood of the game well. The music is also quite nice, especially how it changes depending on your remaining health. It reminded me a lot of Ridiculous Fishing, a game which I love very much. The gameplay is pretty addicting, I found myself trying over and over to reach the final collectible. It would be cool to see new collectibles added as well, like a baguette or something.

I do feel like being able to collect just one gem before automatically returning to the surface feels limiting. I think collecting an unlimited amount before dying would be much more rewarding, although that would imbalance the current pricing system for upgrades. Maybe having new slots to hold items as an upgrade would be a good fix.

The hitbox for the character feels a little too large, mainly on the character's head. I'm pretty sure it accurately fits the character sprite, but I keep surprising myself when a swordfish pokes the top of my head when I think I've evaded it.

Overall super fun game, nice work!