Nagate Tanikaze is the main protagonist of the anime series Knights of Sidonia: Battle for Planet Nine. He was born as a clone of the legendary ace pilot Hiroki Saitou, but was raised in secret by Hiroki, whom he knew only as his grandfather, deep within the underground layers of the generation ship Sidonia. Growing up in complete isolation, Nagate spent his childhood training every day on an old Garde pilot simulator, eventually mastering it without ever meeting another person. After his grandfather's death, he emerged to the surface and was quickly drafted into Sidonia's Defence Force, taking control of the legendary Garde unit Tsugumori.

Because of his unusual upbringing, Nagate is shy, timid, and highly naive, lacking common knowledge about Sidonia's social customs, laws, and technologies. He is also a pure human, unlike most Sidonians who have been genetically engineered to perform photosynthesis and require only one meal per day; as a result, he must eat substantial amounts of food regularly. Despite his introverted and absent-minded demeanor, Nagate possesses a strong inner will to protect the people of Sidonia. His primary motivation is to defend the ship from the alien Gauna and to live up to the expectations placed upon him as the pilot of Tsugumori.

Throughout the story, Nagate proves to be an exceptionally gifted Garde pilot, quickly rising to become Sidonia's top ace. His genetic lineage has granted him enhanced abilities and a form of immortality, which sets him apart from other characters who must undergo artificial treatments to extend their lives. He pilots the Tsugumori and later its custom successors, demonstrating remarkable reflexes and combat instincts. His role in the narrative is that of the unlikely hero who must grapple with his engineered origins, the burden of being a clone, and the political machinations within Sidonia's high command.

Nagate's key relationships include his rivalry with Norio Kunato, the former top pilot who sees Nagate as a threat to his status; his romantic feelings for Shizuka Hoshijiro, a skilled pilot who becomes a close ally; his deep friendship with Tsumugi Shiraui, a human-Gauna hybrid who can change gender and develops strong feelings for him; and his complex dynamic with Captain Kobayashi, who empathizes with him but is often forced by the ruling Immortal Council to send him on the most dangerous missions. Over the course of the series, Nagate evolves from an isolated under-dweller into a confident and capable defender of humanity, learning to trust others and accept his role as Sidonia's greatest protector. His notable abilities include unparalleled piloting skill, exceptional spatial awareness in combat, and the capacity to push his Garde to its limits.