Kousaka Mikan

The youngest sister. She's a super genius who invents robots and other crazy things that often times torments her brother. Although she's a genius she tends to act childish and will often cry to get her way. She insists on bathing with her brother and will become incredibly angry if she can't.

Her inventions allow her to do most anything including spaceflight and time travel.

With the secret underwear patch she wears diapers and nothing else.