Fumitsuki Nanakorobi excels academically as class president while nursing an intense, unrequited crush on Chitose Hitotose. She strategically leverages her class duties to infiltrate his daily life, persistently seeking his attention. This includes joining his rooftop lunches with Minazuki Rokumatsuri, though she privately yearns for solitude with him.

Her forceful personality often erupts in comedic aggression, manifesting as powerful punches directed at classmates or even Chitose himself to silence them or vent frustration, masking her deeper romantic motives. Driven by dogged curiosity about inconsistencies in Chitose's story of living alone—like his punctual arrivals in clean clothes—she investigates, leading to unexpected encounters with his teacher guardians outside school.

Moments of vulnerability reveal a softer side, such as when an accidental fall resulted in unconscious proximity to Chitose, an event she later attempted to exploit romantically. Her relentless pursuit includes a rivalry with Kanna Togakushi, another suitor for Chitose's affection. Fumitsuki's persistence ultimately culminates in a direct confession during the final season. Her name, incorporating "tsuki" (month), aligns with the series' thematic use of traditional Japanese month names.