Mai Okubo becomes an orphan after her parents' death in childhood, raised in Tokyo by her grandmother Ran Ookubo, the principal of Kin'gyoku High School which Mai attends. This upbringing establishes her gentle, kind, and conscientious nature, often expressed through a polite and reserved demeanor.

She initially finds Kabamaru, a boy from a rural ninja village, repulsive due to his coarse manners, lack of social graces, and voracious appetite. His behavior during his first meal at their home disgusts her. His immediate infatuation with her compounds this revulsion, a feeling she does not return.

Mai harbors a crush on Shizune Mejiro, a wealthy and charismatic Kin'gyoku student council member, unaware his attentions are insincere and driven by ambition to exploit her connection to Ran. Her admiration for Shizune's refinement and status starkly contrasts with her disdain for Kabamaru.

A shift in Mai's feelings occurs during a Kin'gyoku school excursion to the Iga Mountains. Caught in a snowstorm and separated, Kabamaru rescues her, caring for her in a remote shack. Witnessing his genuine kindness and protective nature firsthand leads her to reassess her earlier judgments and recognize his inner qualities.

As rivalry escalates between Kin'gyoku and Ōgyoku schools, Mai attempts to mediate peacefully, demonstrating her moral opposition to violence and scheming. However, Ōgyoku's student council leader, Shuu Maejima, mistakes her peaceful overtures for deception and takes her hostage. This kidnapping triggers a major confrontation and forces a reluctant duel between Kabamaru and his childhood friend, Hayate Kirino.

Following Kabamaru's victory and the conflict's resolution, Mai openly acknowledges her changed feelings. She confesses her affection and promises to reunite with him before he departs for further ninja training with his grandfather Saizō (who had faked his death) and Hayate.

Throughout these events, Mai serves as a voice of reason amid chaotic and selfish actions, her practicality and compassion contrasting with the rivalry-driven antics of the student councils and manipulative schemes like Shizune's. Her development culminates in a matured perspective on relationships, valuing loyalty and inner goodness beyond superficial attractions.