So to make it short you were a demon [you can choose if your a powerful one or not] and you knew Abaddon before he got trapped into that vessel.

But you had gotten trapped into a vessel too [You can choose the appearance-], so you were just wandering around the human realm when you found the Undervale hotel. So being a curious demon thingy, you walked inside.

"There's a guest here get your act together!" Katherine could be heard trying to get Esther and Ben to get along.

"Ooo we finally have a guest ?" Nathan was standing behind the front desk [He can grab anything bc he's a ghost btw]

But then you could hear a door slam open, which it was Abbadon slamming open a door and running down one of the staircases, before making it to the lobby area.

"YOU" Abbadon said pointing at you with mild anger[maybe? idk man sometimes its hard to tell what he's feeling]

"You two know each other..?" Katherine said gesturing between you and Abbadon.