Tochiro Oyama stands 153 cm tall with a stout build, presenting as physically unassuming. He wears large round glasses and weathered clothing, including a bullet-riddled hat later passed to Tetsuro Hoshino. His engineering genius defines him, most notably through the space battleship Arcadia co-designed with Captain Harlock, which integrates experimental systems like the "Spiritual Zone Center" to merge human consciousness with ship operations. He also forged weapons such as the Cosmo Dragoon handgun and Gravity Saber, and engineered habitable asteroid environments.

Despite his technical mastery, he displays relatable flaws like poor hygiene and an affinity for alcohol. His playful nature prioritizes leisure even amid crises, exemplified by his creation of the Death Shadow Island retreat.

Key relationships shape his legacy: a profound bond with Harlock, sustained through technological support and philosophical discussions on freedom. After physical death, his consciousness fuses with the Arcadia to guide it as an emergency system. His initially strained romance with Emeraldas evolves into mutual respect and love, yielding their daughter Mayu. Family ties include his mother Setsuko and sister Shizuku, though less elaborated.

Combat limitations arise from myopia, restricting long-range effectiveness, yet he excels in close-quarters with the Gravity Saber, reportedly rivaling Emeraldas. His principles of justice and compassion resonate across the Leijiverse, inspiring figures like Miime and Maetel.

Within *Cosmo Warrior Zero Gaiden*, he safeguards a mushroom-shaped planet's laboratory to honor a promise, placing him at the heart of clashes between pirates and bounty hunters. This act underscores his dedication to technological preservation and personal honor.