So there are two OPM fics in mind currently:
-The first one considers that Genos self-destructed himself to deal with that veiny anomaly in the final battle, and after a year of waiting for his trial, is sent back into the mortal world to ‘finish his unused years, for god damn’s sake’. He technically possesses a dead kid and goes to find Saitama. Shenanigans follow, and eventually Genos loses his self as he merges with his identity of a kid.
-the second one is more or less a OPMxUndertale crossover with the duo falling in while investigating an energy spike. Saitama’s out for the action for most of the fic, and Genos attempts to forge a way to the barrier while having to convince that his name doesn’t mean he’s in for genocide. At the end Saitama just punches the barrier and Flowey rages a lot.
Just kind of inbox me which one you want me to do for Christmas break, and I’ll start working on it.