To understand what the meaning is to the two universes or AUs you have to understand that they're like branch offs. But they still reside close to the main AUs. For example Vampiretale runs alongside Horrortale, Dusttale, and Axetale while SlaveTale and Her Soul, His Determination takes place on the service after the Barrier falls. SlaveTale kind of sees human females as slaves for like being a nanny or a forced laborer but in this AU Sans is kind of turning the idea on its head by saying your not going to do things for me, your just going to be a sex toy, a plaything and Papyrus, his younger brother, yeah Papyrus is line over six feet tall and he's the youngest but anyway, he sees human females as gentle creatures and Papyrus kind of inserts himself in as her big brother to kind of watch over Frisk and make sure Sans doesn't overstep any pain thresholds Frisk can't handle. The first three chapters are basic enough whereas in the fourth one we see our first look at Chara and she is like a sort of spirit but she can't possess a living body. It has to be dead and it's kind of one of the ways I explain Frisk's past why she cut and why she was self destructive. She did some to herself yes, but the bulk of it was Chara. The reason her wounds healed so quick was she has healing magic that she used to repair injuries a little at a time. Sans doesn't know this. Vampiretale is relatively simple. A person/monster goes searching for solace after losing his true soulmate and ends up in a place a lot like his own AU but it's vampire versions of his friends and Ink whom he just saw die in front of him from a fatal disease known only to Ink's kind.
