Hajime Saito, a non-commissioned officer in the United Nations Cosmo Marines, carries a star-shaped scar on his left cheek—a remnant of past combat that mirrors his expertise in close-quarters engagements. His formative years intertwined with Colonel Goro Kiryu’s family, particularly Kiryu’s daughter Mikage, whose brotherly bond with Saito forged his protective instincts and steadfast sense of duty.

During the 2199 Garmillas assault on a lunar base, Saito emerged as the sole senior survivor of his annihilated regiment, bearing witness to Kiryu’s death. His resolve hardened, he confronted Admiral Ryu Hijikata over delayed reinforcements, a defiance that led to temporary exile in Earth’s riot control division. Forced to fire on civilians, his disillusionment erupted into clashes with Earth’s leadership, exposing his unyielding ethics and refusal to compromise principles.

By 2202, commanding the 5th Regiment on the Eleventh Planet, Saito orchestrated evacuation efforts when Gatlantis forces ambushed his unit. Dispatching Master Sergeant Shiori Nagakura to seek aid, he secured their rescue by the Yamato—a testament to his tactical ingenuity and unwavering focus on safeguarding lives.

An alternate timeline casts him as a space marine leader rallying a Yamato mutiny against the White Comet Empire. In its climax, he detonates the Gatlantis stronghold alongside science officer Sanada, trading his life to cripple the enemy—an act etching his legacy as a soldier who valued victory over survival.

Saito’s character thrives on contradictions: loyalty to comrades clashes with a blunt defiance of authority, while his stern exchanges with superiors like Hijikata coexist with a playful, almost brotherly dynamic with Mikage. Across timelines, his core remains unshaken—a soldier anchored equally in duty and the bonds defining his humanity.