Hotaru Amatsuka occupies the position of the fifth daughter within the Amatsuka family, nestled between her older and younger sisters. At 14 years old, she is a third-year junior high school student. Her appearance features brown eyes and shoulder-length brown hair accented by distinctive cheek curls, frequently complemented by a hairbow, and she stands 154 cm tall. Born on February 12th, she is an Aquarius with blood type O. Her personality blends a caring, nurturing nature with a playful flirtatious streak. She openly expresses romantic interest in her older brother Yotarō, often fantasizing about him and self-deprecatingly thinking, "Hotaru is a bad girl." This flirtation manifests in actions like coordinating with her sister Rikka to demonstrate their maturity to Yotarō; they once performed in idol-style miniskirt costumes and pinned him to the floor to prove they were "not little girls anymore," an effort interrupted by another sister. Cosplaying stands as one of her primary hobbies. This interest aligns with her participation in the family's promotional activities, such as appearing in swimwear during a riverside video outing. Her family interactions involve group dynamics, including discussions about physical appearance with her sisters, such as conversations about breast size that inadvertently distress her flatter-chested siblings.