Mai Ōkubo is the granddaughter of Ran Ōkubo, headmistress of Kin'gyoku High School. After being orphaned at a young age, she was raised by her grandmother and resides with her in a large mansion. She attends Kin'gyoku High School as a student.

Upon their first meeting, Mai finds Kabamaru, a boy from a rural mountain village, repulsive due to his coarse manners, unbelievable appetite, and lack of social graces. His messy eating habits particularly embarrass her. For a significant period, she holds an unrequited affection for Shizune Mejiro, a handsome and charismatic student, unaware that his attentiveness stems from her lineage and his own ambitions.

Mai is often portrayed as kind, gentle, and possessing a strong sense of common sense. She frequently acts as the voice of reason among her peers, criticizing immature and selfish behaviors. She prefers peace and calm and maintains a generally optimistic outlook. Her perception of Kabamaru gradually shifts after a significant turning point during a blizzard in the Iga mountains. Separated from her group and rescued by him, she witnesses his tender and protective nature while he cares for her in a shack, marking the beginning of her acknowledgment of her own growing feelings.

Her role deepens as the rivalry between Kin'gyoku and Ōgyoku schools escalates. In an attempt to prevent an all-out conflict, she approaches Shuu Maejima, the Ōgyoku student council president, which results in her being taken hostage under the belief she was tricking him, necessitating her rescue by Kabamaru.

Ultimately, Mai and Kabamaru reconcile. She develops feelings for him after coming to know him better and understanding he is not as she initially thought. She reveals these feelings to him, and they promise to meet again before he returns to the mountains for further training.