Work Text:
Rex is the result of a high school boy: Chad.
He was given three wishes; he wished for the perfect boy friend, not someone to date, a friend being a boy too.
So Rex was magically created, though magic failed to understand that he was supposed to be a friend, not a love interest.
Now Chad's trying to erase him because Eliot has always been his friend.
Chad is literally trying to kill Rex because he never existed in the first place.