Nanase Tsukumo is the homeroom teacher for the class including Yuuta Togashi, Rikka Takanashi, Shinka Nibutani, and Makoto Isshiki. She possesses short brown hair and blue eyes. Her personality is passive, kind, and caring towards her students, always maintaining fairness when addressing disciplinary issues. Tsukumo exhibits a relaxed and professional demeanor during classroom interactions, though a subtly crafty or teasing side occasionally surfaces beneath her gentle exterior. This manifests in habits like stretching out the ends of her sentences or gently provoking students such as Rikka. Yuuta and Rikka refer to her by the nickname "Nana-chan."

Within Season 1, Tsukumo approves the formation of Rikka's "Far East Magical Napping Society – Summer Thereof" club after its members clean a messy schoolroom. She actively facilitates student interactions, for instance suggesting Yuuta walk home with Rikka due to her unfamiliarity with the area. Tsukumo impartially addresses behavioral issues, summoning students like Yuuta for discussions about school matters. Her involvement throughout the series, including Season 2, films, and OVAs, remains consistently limited to homeroom duties and supportive faculty interactions, with no significant character development, background story, or expanded role documented in these later media.