This is an amazing game. I played it a bunch. My understanding is that this game was made by since Japanese student by himself.
It was a free game, but they remastered it at least once, but I think they did it twice.
It’s a Metroidvania style game.
It has a near mechanic where you’re weapon gets more powerful the longer you go without getting hit.
It’s pretty easy to power up your gun, so it’s not a huge loss if you do get hit. The music is also pretty decent.