This was cute. The lack of any info on controls was frustrating, but I pressed things, assuming WASD, and figured out the swing and shoot (Z and X). I did not figure out how to absorb (hold C) until reading comments here, after beating the boss. I was getting ready to give up when we found the portal to the boss, and retried by avoiding everything and going right to it. The swing attack was really effective, and I managed to beat it with a just a bit of energy to spare. After reading the comments I went back and tried using C to absorb, and also ended up repairing some of the broken spheres, which look like they use some energy to repair, but then give you an energy regen. This game looks like it has a lot of potential.
For any future jams you do, I'd recommend giving info on the controls, even if it is just on your Itch.io page. You can update the text of the page after submissions close, so you can focus on the game until the deadline, and then go back to add any useful info about the game.