You lived with a skeleton demon monster, or to be more precise with Fell Sans. He was shorter than you and you often joked about his height. Now Fell went to grillby and you sat in the library and read different books until you came across one. It was called "All about Demons and their types." and you started reading it. You stopped on one page and there was a view of Fell.

"A type of demon-monster. Such demons are more powerful and better at controlling magic. Demons of this type can grow from the happiness they feel."