There is someone who can travel in-between dimensions. Such a way that he can see and interact but the others can’t see him however can touch him.
They can also see him through a mirror only
The technology that allows him to do that comes from another race that got destroyed.
He spends his days doing pranks. Starting wars.
He fell in love of a human who stole part of her power. She was hoping to find another dimension where her parents are still alive and she isn’t.
Still not sure..