Himari Takakura is the younger sister of Kanba and Shoma Takakura, a girl approximately thirteen years old with long light orange hair and purple eyes. Her life is defined by a terminal illness, a brain tumor that has led to repeated hospitalizations and a prognosis that offers no hope for recovery. Despite the severity of her condition, Himari is characterized by her cheerful and optimistic demeanor. She makes a conscious effort to smile and maintain a positive attitude, primarily to ease the worry of her two brothers who care for her. Her personality is typically calm, kind, and curious, and she devotes her energy to simple domestic tasks, finding joy in cooking, cleaning, and knitting as a way to live fully within her limited circumstances.

The central event that drives the story forward is Himari’s collapse and apparent death during a trip to the aquarium with her brothers. She is miraculously revived by a penguin-shaped hat purchased from the aquarium’s souvenir shop. This hat contains the spirit of the Princess of the Crystal, who extends Himari’s life. However, this extension comes with a severe condition: in exchange for keeping Himari alive, her brothers must locate a mysterious item known as the Penguindrum. When Himari wears the hat, her entire personality and appearance change, transforming into the domineering and authoritative Princess of the Crystal, who has no memory of Himari’s own experiences or relationships.

Himari’s background reveals that she is not biologically related to Kanba and Shoma. She was an unloved child who wished to disappear from the world before Shoma brought her into the Takakura family. After being abandoned by her own mother, she was taken in and became a beloved daughter in the household. A significant part of her past includes her friendship with two girls, Hibari and Hikari, with whom she planned to form an idol group called Triple H. Her failing health prevented her from joining them, but she harbors no jealousy over their subsequent success as the duo Double H and expresses genuine happiness for them.

In terms of her role, Himari is the emotional and motivational core for her brothers. Her impending death is the catalyst for all their actions as they desperately seek the Penguindrum to save her. She is largely unaware of the supernatural bargains being made on her behalf or the true nature of her survival, believing simply that her life has been prolonged by a miracle. Her key relationships are intensely familial. She loves both of her brothers deeply and wants to protect them from pain, though she does not fully grasp the dangerous lengths to which they are willing to go. Her bond with Shoma is particularly profound, as he was the one who first brought her into the family and shared the fruit of fate with her. She considers him her fated one. Her relationship with Kanba is equally strong, and she eventually tries to sacrifice her own life to prevent him from committing terrible acts to save hers. She also befriends Ringo Oginome, seeing past the girl’s eccentricities to find a genuine and kind person, making her a trusted confidante.

Himari undergoes a notable development from a passive recipient of her brothers’ protection to an active agent in her own fate. Initially, she simply accepts her illness and the miracle that saved her. However, as she witnesses the destructive paths her brothers are taking, she begins to resist their sacrifices. She matures beyond her role as the sick sister who needs saving and attempts to take control of the situation, even offering to return the life that was given to her if it means stopping Kanba. Her abilities are not magical or combative; instead, they are the skills of a homemaker, including cooking, embroidery, and knitting, which she uses to care for her family and create a warm, stable home environment despite the chaos surrounding them.