This is mostly just crossover versions: Fallout, The Last of Us, Battlefield, Destiny, Sword Art Online/Gun Gale Online, SCP, and lots of other genres and verses.
Yeah, PG-13 content isn't necessarily a +18 rated RP type, but does seem to include subjects that could be delicate, but not +18 such as accessive kissing or minor violence. There should be a specification on a few things like that.