Sumiko Kawai oversees Kawai Complex, a boarding house managed in place of Ritsu Kawai’s absent parents. As Ritsu’s grandaunt, she meticulously vets prospective residents, upholds dormitory rules, and crafts meals tailored to individual tastes. Though she presents as a cheerful, observant elder with a calm demeanor, she privately embraces a self-styled role as a matchmaking bystander, discreetly nudging tenants like Kazunari Usa with romantic advice. Beneath her affable exterior lies a strict disciplinarian unafraid to reprimand or physically correct misbehaving residents like Shirosaki or Sayaka.

Her playful side emerges when teasing Kazunari over his crush on Ritsu, though she often shields him from consequences during others’ mischief. Pragmatic and protective, she equips female tenants with self-defense tools to deter harassment. A collector of dolls and secret enthusiast of love stories, she subtly mirrors these interests in her interactions. While her personal history remains undisclosed, her unwavering commitment to balancing eccentricity with order cements her as the dormitory’s steadfast anchor, maintaining harmony without deviating from her established, enigmatic role.