Kazusa Himuro leads Green Ship, a stunt group publicly presented as a training school for thrill-seekers and performers. Secretly, Green Ship functions as an assassin training camp operated by the Tojo yakuza group, with Kazusa serving as the organization's chief enforcer. This position grants him significant authority over both the group's legitimate stunt activities and its covert assassination missions.

He develops a physically and emotionally intimate romantic relationship with Tomoe Oujima after she joins Green Ship. This connection complicates when Tomoe uncovers Green Ship's true assassin-training purpose. Demonstrating his ruthless nature, Kazusa executes an undercover policewoman who revealed the organization's secrets to Tomoe, forcing Tomoe to flee.

Following Tomoe's defection and her alliance with Iori Tojo – the heir to the Tojo group whose stepmother hired Green Ship to eliminate him – Kazusa becomes the primary antagonist pursuing them. He coordinates efforts to eliminate Iori and fulfill the assassination contract. Despite this antagonistic role, Kazusa adheres to a personal code reminiscent of samurai honor. This code culminates in a final confrontation where he challenges Iori to a traditional sword duel amidst the burning ruins of Green Ship's headquarters.

His motivations remain largely unexplored, with no detailed background or internal conflicts provided beyond his dedication to Green Ship's objectives and his complex, ultimately doomed relationship with Tomoe. The character arc concludes with this climactic duel, resolving his role in the conflict.