Kokusai is the student council president at Senzoku High School and a second-year judo club member. He trains in judo and maintains a friendship with his classmate Akutsu. Kokusai possesses a shy and somewhat absent-minded personality, frequently feeling embarrassed in social situations while remaining unaware of certain social cues or the reasons for others' behavior towards him. He lives with his grandmother, who is often away during the day.

An unintentional aspect of Kokusai's life involves attracting unwanted male attention, particularly enduring repeated sexual harassment during subway commutes. This vulnerability leads him to confide in Chiga, a junior judo club member whom he later appoints as his vice president. Kokusai initially hesitated to appoint Chiga, concerned he would take the role too seriously and become burdened, but did so after direct prompting.

Their relationship evolves beyond the senior-junior dynamic. During a joint outing to a barbershop, Kokusai wears new clothes, mirroring Chiga's effort to dress well for their meeting. Their interaction shifts significantly when Chiga initiates a kiss; Kokusai responds positively and later reflects on his growing feelings. This development creates subsequent awkwardness in their communication, which Kokusai attempts to navigate.

A concerning pattern emerges regarding Kokusai's safety. Returning home alone after the outing, he discovers his apartment door unlocked despite no recollection of locking it, though the windows are secured. He falls asleep on the couch while talking to Chiga on the phone. An unknown man, previously observed watching Kokusai and Chiga during their outing, approaches him while he sleeps. This intruder leaves physical signs of sexual assault, discovered later by Chiga upon his arrival.