Kyouhei Kashihara occupies the weapons officer post aboard the submarine I-401 within the mercenary group Blue Steel. He directly operates the vessel's diverse armament systems, including photon cannons, missile launchers, torpedo tubes, and the salvaged Super Graviton Cannon during combat.

His personality presents a distinct contrast between routine duties and high-stress combat. During standard missions, he exhibits professionalism in managing weapons systems. However, Captain Gunzou Chihaya's high-risk tactical maneuvers frequently trigger visible panic; Kyouhei often crouches in his seat, vocalizing fears of failure or destruction. This reactive nature coexists with his tendency to voice socially inappropriate comments, occasionally sparking friction among crew members.

Academically, he ranked approximately 200th in his class at the Japanese National Maritime Institute of Technology, placing him significantly behind crewmates who held positions within the top ten. Outside his professional responsibilities, he maintains an extensive personal collection of gravure idol merchandise, a recurring character detail.

His specific background prior to joining the I-401 crew remains undefined. He joined the crew roughly one year after Gunzou Chihaya and Iona escaped from Yokosuka, alongside engineering officer Iori Watanuki and first mate Sou Oribe. Relationships with other crew members stem primarily from operational interactions rather than deep personal bonds.

Across all documented media—manga, anime series, and films—Kyouhei's core role and personality traits remain consistent. His personal narrative lacks significant evolution or transformative development throughout the series' events. His function centers on weapons operation and providing comic relief through exaggerated reactions to danger. No concrete information details his activities or character progression in spin-off materials.