Jasper is a self-styled phantom thief and treasure hunter. He travels the Nightmare Realm in search of valuable items for his collection, though he also makes it a habit to give away his spoils to people who need them. While he often gets into trouble for his treasure-seeking activities, he always manages to escape with his life (and good humor). He teams up with Kuu and their Treat friend Mimi to form a sort of pirate squad in search of loot.

He has the special ability to influence luck, which makes him a terrible opponent in games of chance. Because of this, he is also banned from most casinos.

He is very short (158cm or 5'2"), and his lack of height has always been a sore spot for him. He also really dislikes it when people point that out.