ok but i'm a sucker for bOTH OF THEM so: underfell sans meeting underswap papyrus and he's just like "oH GREAT IT'S YOU AGAIN" and papyrus is just like "?? chill" and sans realizes that. not all the papyruses are the same. most of them are?? cool?? and not total dicks?? and underswap pap just kinda adopts him as his second brother by accident and when underswap sans asks him why there's an edgy red guy calling him bro he just shrugs and goes "whoopsy doopsy"