Kanako Sasa attends elementary school as a fifth-grade classmate and friend of Shuichi Nitori and Yoshino Takatsuki. Her childhood connections include knowing Yoshino since preschool and later befriending Saori Chiba and Chizuru Sarashina. Physically, she possesses brown hair typically arranged in twintails with ribbons, brown eyes, and a notably short stature that lends her a younger appearance than her actual age.

Her personality emphasizes empathy and an active pursuit of harmony within her social circle. She intervenes in disputes, especially tensions between Saori and Yoshino regarding their affections for Shuichi, and experiences visible distress during peer conflicts. Kanako maintains an energetic, cheerful disposition with a generally optimistic outlook, though she demonstrates naivete and resists deep reflection, often citing that overthinking causes her "brain itch" or headaches. She places supreme value on friendships and family, consistently showing minimal interest in romantic entanglements.

Family interactions reveal her indecisiveness and childlike reliance; her mother handles daily tasks like choosing Kanako's outfits and assisting with morning routines. Her younger brother coins her nickname "Kanabun" (drone beetle), later adopted by Chizuru. Academically, she joins the junior high volleyball club alongside Saori, reflecting her active yet conventional inclinations.

During the high school transition, Kanako enrolls in an all-girls institution, leading to diminished contact with junior high peers due to separated educational paths. Her presence within the friend group lessens as their lives diverge, though her core supportive and conflict-avoidant nature persists unchanged.