Ok everyone, hear me out:
An Iron Giant/One Punch Man AU! where Genos comes crashing into earth from some unknown planet, is glimpsed throughout the small town he lands in and is thought to be a monster, is full of highly sophisticated weaponry, and can’t remember where he really came from or what he is.
He’s rescued by Saitama (who in this is a recluse who owns a junkyard, or a line cook at a local small town diner, or something on those lines), learns through him that he has a soul and falls in love.
(I’d like to think that in this Genos would be on the same level of communication as the giant, able to talk in bits and pieces and able to understand things in his own way, partly because of some kind of dent in his body, partly because he was in fact designed to be a weapon.)