Only took me 12 hours but I finally have an idea that is worth it.

You’re a virus in the blood stream and must infect everything SHMUP style.

Doesn’t sound like much but the glory is going to be in the gameplay mechanics. Every antibody you infect you can become, and every antibody you become slowly dies because it is infected. The rush to infect and become the next enemy before the current one dies will give the game that “je ne sais quoi” that I’ve been looking for.