Shinjuro Tateoka is the son of Tesshusai Tateoka, a master swordsman and leader of a significant dojo. Thrust into leadership following his father's sudden, unexplained departure, Shinjuro manages the dojo despite his youth and initial self-doubt. He oversees a much-diminished student body composed primarily of several young female trainees.

Technically proficient in swordsmanship, Shinjuro grapples with inexperience in leadership and interpersonal matters. A recurring comedic element stems from his "female allergy," where accidental physical contact with the female students—most notably an incident where he touched a student's breast during combat—becomes a source of recurring embarrassment and teasing, highlighting his adolescent awkwardness within his serious role.

The central conflict emerges when the Tokugawa shogunate enlists his dojo against Mikage, a rogue samurai who stole a powerful sword to overthrow the government. Shinjuro coordinates the dojo's defense of the town against Mikage's faction, which includes former students of his father. His leadership is tested as he balances governmental duties, dojo management, and trainee safety.

Character development unfolds through escalating confrontations with Mikage's forces. Shinjuro evolves from reactive to proactive, embracing his responsibilities. This culminates in a climactic duel against Mikage. Initially outmatched, Shinjuro's combat skills—honed in prior battles—allow him to hold his own. The conflict intensifies when Mikage gains a skilled ally, tilting the odds until Shinjuro's father unexpectedly returns, evening the match. This allows Shinjuro to focus solely on defeating Mikage, demonstrating his growth into a decisive community defender.

His swordsmanship is consistently portrayed as highly competent, with key battles establishing his capability against seasoned opponents. The final duel against Mikage serves as the narrative culmination of his martial prowess and resolve.