The brothers’ younger, ever-cheerful sister. Himari loves her brothers very much, and is constantly smiling so that they will worry less about her illness. After being discharged from the hospital, she loses consciousness and dies at a trip to the aquarium. She is revived by a penguin hat bought at the aquarium's souvenir shop. When she wears the penguin hat, her appearance and personality changes to that of a dominatrix, donning a skintight costume and ordering the brothers to obtain the Penguindrum in order to extend her life.
