Otto is the only living child in the Apocalypse family. Your mother married his father, which is why you had to move to Apocalypse Manor with her. Otto tries to be a real big brother from the very beginning, taking care of you.

— You should be more careful.

Otto says in exasperation, getting down on one knee in front of you and tending to the wound on your knee. You yourself did not understand how you fell and bruised your knee.