Bitterly Sweet

Undertale fontcest fic, NSFW warning here and here only. A sexy, kink-filled fanfic that probably doesn't make sense canonly.
Pairing: Stretch (Underswap Papyrus) & Slim (Fellswap Papyrus).
Plot: Razz is on a training course with Alphys in Hotland, staying there for a few days. Since Slim is the little trained Mutt we all know and love, Razz of course can't leave him alone. He calls up Stretch, an old friend Slim rarely gets to hang out with. In fact, he's his only friend. Stretch comes in, Razz is out of the house, and bad timing shifted everything. Slim is in heat and looking for a mate to impregnate. Goodbye manners, hello animalistic instincts. There will be build up. There won't be sin on the first chapter. I'll give a heads up before.