Chigusa Mizusawa, widowed aunt to Kasumi Kishimoto, manages the Hidamari Private Boarding House, a residence for male students of Myōjō High School. Following her husband’s passing, she converted her home into the boarding establishment, a choice initially concealed from Kasumi, who unknowingly moves in after enrolling. This arrangement establishes the shared living environment where Kasumi navigates daily life alongside four male tenants, including Yūsaku Takasugi.

Chigusa’s late husband was the brother of Katsuhiko Muraki’s father, linking Katsuhiko to her as a nephew by marriage and Kasumi’s cousin. While Katsuhiko resides primarily in the United States, Chigusa maintains her role as a stabilizing presence, fostering communal bonds within the boarding house that nurture the characters’ interpersonal growth.

The anime adaptation reinforces her pragmatic yet approachable nature, introducing subtle nuances such as her decision to welcome new tenants like Maria Ōta and Maria’s father—the latter’s charm playfully influencing Chigusa’s approval. Though her direct interactions with boarders often occur offscreen, her oversight shapes the household’s dynamics, anchoring the narrative’s focus on shared coexistence.

Across official media, including the anime film sequel, Chigusa’s background remains focused on her identity as a maternal landlady. Her narrative purpose centers on sustaining the boarding house as a foundational space for relational development, with no elaboration on her personal history or evolution beyond this role.