Kouichi Tsuruuchi is a senior Gardes pilot aboard the generation ship Sidonia, originally serving as a member of the Samari Squad and later leading his own Tsuruuchi Squad with the unit designation 007. In social settings he comes across as easygoing and informal, often making crude jokes and directing teasing remarks toward his commanding officer Samari Ittan. His personality shifts markedly once he enters combat, where his confident and playful demeanor gives way to a focused, aggressive pilot who nonetheless tends to be reckless and overly reliant on the Heigus Particle Cannon. Tsuruuchi participates in several critical operations, including the defense against Gauna 487, the joint rescue of Nagate Tanikaze and Shizuka Hoshijiro, and the final battle against the Large Mass Union Ship. Throughout the series his motivation remains the survival of Sidonia and its people, and while he does not undergo a dramatic personal transformation he proves himself a dependable and formidable ally in the most harrowing battles. His key relationships revolve around his squadmates, particularly Samari Ittan, whose repeated and often comical rejections of his advances become a running gag, and his growing respect for fellow pilots like Tanikaze. His notable ability is his refined piloting skill, which makes him a dangerous combatant even if his impulsive streak sometimes puts him at risk.