My friend and I's project was originally conceived as a "single-stick" shooter (a take on twin stick shooters) with only one stick and one projectile. At first we imagined the player as an archer that would move themselves by firing arrows, but that didn't make a whole lot of sense. We ended up adopting a sci-fi aesthetic, so the idea of moving the character with the projectile's recoil was on the page again. As we built, more and more elements fell nicely into the "Only One" theme. We have one persistent boss enemy, one stage, one life, etc.