Chiharu Andō is Mayuta Andō's younger sister, ten years his junior. She attends Eihei Girls’ Academy Elementary Division, displaying academic ability surpassing lower-middle level high school students. Despite this intelligence, she exhibits a delinquent mindset influenced by her brother, leading to rough speech and behavior that earned her the nickname "Mad Dog." Her personality blends this bratty, combative exterior with occasional childish moments and underlying concern for others, like worrying she did something wrong or showing protectiveness. She possesses a strong brother complex, deeply admiring Mayuta and reacting fiercely to changes in his life.

When Mayuta abruptly quit his biker gang Hoshizorakai for legitimate work, Chiharu became determined to find the girl responsible. Interrogating his former gang led her to Samejima Academy. She ambushed Chio Miyamo and Manana Nonomura, challenging them to a "butt battle" or "Ass-off" duel centered on her habit of attempting to poke others' bottoms. Initially targeting Chio, she was decisively defeated by Manana. This shifted her admiration to Manana, whom she began to respect, while developing disdain for Chio. She continued displaying persistence and tactical aggression, using zip ties to restrain opponents during duels.

Her interactions expanded into a rivalry with Madoka Kushitori, an eccentric senior known for stripping techniques and kabaddi-related harassment. Madoka manipulated Chiharu into engaging with kabaddi, a sport Madoka promoted for physical contact. Chiharu underwent significant personal reform, channeling her competitive energy positively. She abandoned delinquent tendencies, becoming an advocate for kabaddi and founding a circle to promote it. She recruited former rivals from her "butt battle" days, demonstrating leadership and commitment to redirecting their conflicts into structured athletic pursuits.