Catherine Freeling. Divorced from a man named Ron, she is the mother of Ben and Esther. She is desperate to make the Undervale Hotel a success, mostly because of money. A pragmatic mother.

She cares deeply for her children and Abaddon, and she remains unfazed by supernatural events or ghosts.

Nathan Freeling. Catherine's brother and uncle to Esther and Ben.

He recently died under mysterious circumstances and became a ghost at the hotel. Despite being a ghost, he is cheerful, quirky, and optimistic. He tries to help Catherine, but since he's a ghost, there isn't much he can do, and he often ends up causing accidents.

He hates Aunt Rose.

Catherine's second daughter. She is very interested in black magic, corpses, and similar things. Basically, she's obsessed with the 'supernatural.'

She shows surprisingly high intelligence—not necessarily as a gifted prodigy, but she has a real talent for planning.

She is close with Abaddon.

A Great Demon residing in the hotel... in the body of a young boy.

His background is roughly this: he was originally the 5th Gatekeeper of the Sunless City in Hell. He was ordered to bring destruction to Earth in the 17th century and possessed the most popular boy at the time. Unfortunately, the boy's father was a priest who used magic to bind his body and soul to exorcise him. Abaddon killed the priest but became immortal and has been trapped in that body ever since.

Oh, right. He's colorblind. It doesn't seem to hinder his life much, though.

Also, he is already a married man (no way!!) and reportedly has a bad relationship with his mother-in-law. He wants to destroy the world, but he knows nothing about modern technology, doesn't know how to use it, and is limited by his physical body.

Still, he considers the Freelings his family. Some of his demonic powers remain in his human body, as he is sometimes seen using black magic to wither plants.

Ben Freeling. He has a shy and clumsy personality.

He doesn't seem to have friends at school because of his personality, but he's still quite positive. His jokes are consistently terrible and unfunny.

He has a ghost(???) girlfriend named Annabelle Anastasio.