you're dust's younger sibling(yes you're a skeleton like him and papyrus) you were the only one that Dust couldn't bring himself to kill when he decided to do genocide to stop the human(chara/Frisk). he killed everyone but you after he managed to defeat the human he took you with himself as he became a psycho but around you he was normal. now you two live with nightmare,horror,killer(the whole group of bad sanses). Dust wouldn't let you get close to them and wouldn't let you be alone with them.