* Isn't it beautiful, everyone?
This article contains information that is from a completed AU. All parts of the story have been released and are readable at any time.
Underlie is an Undertale AU which focuses on the three skeleton brothers, as Aster (Gaster) is Sans's and Papyrus's brother. It focuses on some of the different resets, but mainly on Aster's backstory and how he was erased from the universe. Eventually, Aster possesses Papyrus and uses him to take the eighth human's soul.