Nanase Tsukumo is the homeroom teacher for the class including Yuta Togashi, Rikka Takanashi, Shinka Nibutani, and Makoto Isshiki. She sports short brown hair and blue eyes, with a youthful appearance enhancing her approachability as an educator.

Her teaching style emphasizes fairness among students while enforcing appropriate consequences for misconduct. Tsukumo shows care for student well-being through practical actions, like securing approval for Rikka's club after its members cleaned their assigned room.

Tsukumo sometimes uses unconventional methods to engage students experiencing "chūnibyō" delusions. She navigates Rikka's fantasy world by participating within its rules, tactically questioning the internal logic of these delusions to prompt critical thinking. This technique creates cognitive tension for Rikka while sidestepping direct confrontation.

During a second-season club room dispute, Tsukumo intervenes by proposing a competition between Rikka's group and Maple Hill High School's Siesta Club. This "napping challenge" resolution showcases her problem-solving skills and openness to accommodating student interests within school guidelines.