Kyohei Kashihara studied at the Japanese National Maritime Institute of Technology alongside classmates Gunzou Chihaya, Sou Oribe, and Iori Watanuki. Ranking around 200th academically in his year contrasted with the top-ten placements of most crewmates, yet he consistently secured top-ten positions in gunnery and sea mines, an observation made by Sou Oribe.

He later became the weapons officer aboard the submarine I-401, operating its torpedo tubes, photon cannons, missile launchers, and salvaged Super-Graviton Cannon, favoring direct assault over stealth.

Kyohei exhibits a straightforward personality and often boosts crew morale during tense moments. His hobbies include watching anime, particularly "Maho Shoujo" genres, which he occasionally shares with Iona. An anime adaptation incident shows him attempting to flirt with Iona upon their first meeting. Despite extended service alongside her, he remains wary of her loyalties due to her maintained connection to the Fleet of Fog's communication networks.

His appearance features brown hair typically styled in three upswept ponytails, green eyes usually covered by orange-tinted goggles, and a tattoo on his left shoulder. He commonly wears khaki singlets—sometimes displaying anime logos—dark-blue jeans, and distinctive boots. His role remains operational within the I-401 crew.