Nanase Tsukumo is the homeroom teacher for Yuuta Togashi, Rikka Takanashi, Shinka Nibutani, and Makoto Isshiki's class. She has short brown hair, blue eyes, and maintains a professional appearance fitting her role. Her personality blends a passive demeanor with authentic concern for her students; she interacts fairly while consistently enforcing appropriate consequences for errors or broken rules.

Her supportive yet pragmatic nature is evident when Rikka Takanashi applies to form the "Far Eastern Magical Napping Society of Summer" club. The initial application lacks the necessary members. Instead of rejecting it outright, Nanase Tsukumo assigns the group the task of cleaning a messy school room. After they successfully complete the cleaning, she formally approves the club, ensuring its continuation.

Students like Yuuta and Rikka use the informal nickname "Nana-chan" for her, reflecting a degree of approachability within the student-teacher dynamic.