Mamoru Kodai is an Earthling officer in the United Nations Cosmo Navy and the older brother of Susumu Kodai, the main protagonist of the Space Battleship Yamato series. Born in Kanagawa Prefecture, Japan, he lost his parents to Garmillas meteor bomb attacks early in life, leaving him and his younger brother as each other’s only remaining family. Despite his youth, Mamoru graduated from Space Defense College and, as the war situation grew increasingly dire, was given command of a destroyer—a testament to his competence and the desperate need for experienced officers.

He initially served as a weapons officer aboard the space battleship Kirishima, where he became the first Earthling to fire a shock cannon during the Second Battle of Mars. Later, he was appointed captain of the destroyer Yukikaze, a missile ship. In the opening of the story, Mamoru appears to sacrifice his vessel to cover the escape of Captain Juzo Okita’s flagship during a devastating battle near Pluto. His presumed death serves as a primary motivation for his younger brother, who initially blames Okita and is driven by a desire for revenge. In truth, Mamoru’s ship crash-landed intact on Saturn’s moon Titan, and he was captured alive by the Garmillas. While being transported as a prisoner, his ship crashed on the planet Iscandar. There, Queen Starsha Iscandar healed his wounds and, over time, the two fell in love. Mamoru chose to remain on Iscandar, and the couple had a daughter named Sasha. This decision placed him far from the war, living in peace, but it also kept him separated from his brother and the ongoing conflict.

Mamoru is defined by a deep sense of duty, honor, and personal responsibility. His choice to stay on Iscandar reflects a desire to protect and build a new life rather than continue fighting, yet he never fully abandons his sense of obligation to humanity. His motivations are rooted in love for his family—both his brother and his new family on Iscandar—and a conviction that survival and hope are worth preserving. In Be Forever, Yamato, Mamoru ultimately sacrifices his own life to save Admiral Heikuro Todo from execution, a final act of selflessness that underscores his enduring commitment to Earth and its people.

Key relationships include his bond with his younger brother Susumu, which shapes much of the emotional undercurrent of the series; his friendship with the Yamato’s chief science officer, Shiro Sanada, who respects Mamoru and later takes a protective interest in Susumu; and his connection to Captain Okita, who regards Mamoru’s loss as a profound regret. His relationship with Queen Starsha is the most significant personal development, as it transforms him from a soldier into a husband and father, giving him a new purpose beyond combat.

Over the course of the series, Mamoru undergoes a transformation from an active-duty officer presumed dead to a survivor who chooses peace, and finally to a martyr who sacrifices himself for others. This arc highlights growth from youthful duty-bound soldier to a man willing to give everything for those he loves. Among his notable abilities, Mamoru is a skilled ship commander, a capable weapons officer, and possesses strong tactical instincts. He is also marked by a resilient spirit, able to endure captivity, injury, and the emotional weight of leaving his former life behind. His given name, meaning to protect, reflects his defining trait. Originally, the character was planned to reappear under the guise of the space pirate Captain Harlock, though this storyline was cut due to a shortened episode count.