Haruko D. Dieckmann, whose full name is Haruko Daniela Dieckmann, is a supporting character in the series. She is the biological mother of Haru Kaidou and is also the person who found and adopted Ren Kaidou. Her background is international; she is half-Japanese but was born and raised in America.

In terms of personality, Haruko is depicted as a very eccentric and energetic individual. She is a popular novelist, and her profession contributes to her being almost constantly occupied with her work. This busy nature is a key aspect of her character. Her physical appearance is distinctive; she is a beautiful woman with platinum blonde hair that she typically ties up in a bun, and she has amber eyes. She is usually seen wearing thin, silver glasses.

Her role in the story is primarily defined by her relationships with her sons. As the mother of Haru and the adoptive mother of Ren, her actions and presence are significant to their backgrounds. No verified information is available regarding her specific motivations, her character development throughout the series, or any notable abilities she may possess beyond her profession as a writer.