Ruka is Noelle's younger sister, an elven-looking member of their non-human family. She serves as the family's dedicated mad scientist, constantly designing and constructing mechanical devices to help Noelle fly and achieve her goal of becoming an angel. These inventions are central to her role within the family and the series' events.

Staunchly committed to scientific principles and rationality, Ruka dismisses emotional or non-empirical concepts. This is evident when encountering Eros, a demon-like henchman serving Silky. She seeks the empirical source of his speed but rejects his claim that love powers it, deeming this explanation unscientific. Her frustration with such ideology peaks later, leading her to physically assault Eros after he insults her scientific mindset.

Residing within Yuusuke's unconventional household, Ruka adds to the chaos through her experiments. She maintains minimal interactions with other family members beyond her primary focus: her scientific pursuits supporting Noelle. She also forms an acquaintance with Eros and Muse following their accidental encounter.

Ruka's origins are not explored, and she exhibits no significant evolution throughout the series. Her role remains static: the family inventor, defined by her scientific endeavors and unchanging place within the adopted family unit.