Sakutarō Kirara, aged 17 and in his second year of high school, is Airi Kirara's older brother. They reside together in a detective agency setting, their father often absent due to work and their mother living overseas. Sakutarō possesses a highly analytical and scientifically driven mindset, firmly believing logic and invention solve any problem and initially rejecting magic. This skepticism drives him to create technological solutions like the household chore robot Mechapet as an alternative to the Jewelpets' magic. He dedicates himself to constant experimentation and invention within their home. Tall and thin, Sakutarō often hunches over and wears glasses concealing his green eyes. His appearance undergoes a notable transformation when he removes his glasses, revealing a more conventionally attractive look described as "Beautiful All Along," altering how others perceive him. His character development involves gradually accepting the Jewelpets Luna, Labra, Larimar, and Ruby as part of the household, shifting from viewing them as disruptions to acknowledging them as family. Romantically, Laura Fukuōji, heiress of a wealthy family and Airi's childhood friend, harbors a persistent crush on him and actively schemes to get closer, often aided by Luea. Concurrently, Sakutarō begins developing feelings for Luna, creating romantic tension between Laura and Luna. He participates in narrative scenarios, including a fractured fairy tale parody where he embodies a Cinderella-like figure at Laura's party. Ruby magically provides him with temporary prince-like attire using body paint, which inevitably fades, forcing him to leave the event early to avoid embarrassment. This incident underscores the clash between his scientific worldview and the unpredictable magic surrounding the Jewelpets.