Kiroku Nanbu (Hideki Takahashi) is a Catholic, teenager attending a military-tooled middle school in 1935 Bizen, Okayama. Living in a boardinghouse, he is infatuated with his landlady’s chaste daughter, Michiko (Junko Asano). Unable to express his feelings or quell his libido with masturbation, due to peer pressure, shyness, and Catholic guilt, Nanbu turns to the only outlet left available to him: crazed, brutal violence.
Taken under the wing of Turtle (Yusuke Kawazu), Nanbu is taught how to fight through an elaborate training regimen. He then joins a school gang, the OSMS. A conflict between gang leader Takuan (Mitsuo Kataoka) and Turtle ensues concluding with Nanbu’s usurpation of OSMS leadership. Setting a more aggressive manifesto of actively breaking all school rules, and avoiding girls entirely, he has a run-in with the school drill sergeant and is suspended. Turtle speaks to the school administration on Nanbu’s behalf resulting in both students fleeing Okayama, leaving Michiko behind.
Now living in the Aizuwakamatsu, Fukushima with his aunt and uncle Nanbu reenlists in school but is repulsed by his classmates weakness. He forms a new group and heightened conflicts commence with a local gang. Michiko visits to say goodbye to Nanbu and tell him that she has decided to join a convent as she is unable to bear children. She is later waylaid by marching soldiers. Distraught to new heights, Nanbu spots a poster for (real life) radical, political activist, Ikki Kita (Hiroshi Midorigawa), who he had met briefly in a tea house, and, reinvigorated, marches on to join in the events of Ni-niroku jiken.