Tochirō Ōyama appears across multiple Leijiverse narratives with consistent core traits despite varying backgrounds. In "Arcadia of My Youth," his ancestor Toshiro Oyama serves as an Imperial Japanese Navy technician in WWII Germany, designing optical machinery such as gun sights. He meets German pilot Phantom F. Harlock II, bonding over shared disillusionment with the war. During an escape attempt to Switzerland, Toshiro sacrifices himself mid-flight, using his body to repair damaged plane controls and ensure their survival. Harlock II gifts him his Revi C-12D gunsight as a token of friendship. Toshiro pledges eternal friendship between their bloodlines before Harlock II returns to face the consequences. Centuries later, Tochirō emerges as a disheveled beggar under Illumidas occupation, secretly a Solar Federation engineer. He reveals his rebellion by constructing the spaceship Arcadia in an underground cavern, naming it to honor the ancestral Harlock-Oyama bond. His technical expertise proves vital in the resistance, aiding Captain Harlock and Emeraldas. He repairs Emeraldas' ship after it sustains damage crossing the Flame Stream Prominence and modifies weapons during the uprising. Following the Illumidas defeat, he joins Harlock's crew in exile from Earth. His engineering genius extends beyond the Arcadia; he designs potent weaponry like the Cosmo Dragoon handgun and creates habitable environments within asteroids. Though physically limited by myopia and short stature, he excels in close combat with weapons like the Gravity Saber, matching Emeraldas' skill. His personality blends tenacity with idealism, often masking strategic thinking with humor or apparent foolishness. He champions waste and leisure as necessities, embodied in creations like Death Shadow Island. Key relationships define him. He shares a profound bond with Harlock, rooted in ancestral loyalty and mutual respect. Initially awkward around women, he develops a romantic relationship with Emeraldas, fathering a daughter, Mayu. Ultimately, his consciousness is uploaded into the Arcadia's computer system, allowing him to guide Harlock posthumously as the ship's AI, symbolizing his enduring commitment to their journey. Alternative portrayals exist. In "Gun Frontier," he is reimagined as a samurai searching for a lost Japanese clan in the American West, wielding a shikomizue and displaying comedic traits like poor marksmanship, though his loyalty to Harlock, depicted as a gunslinger, remains central. In "Endless Orbit SSX," he actively serves on the Arcadia crew, develops unrequited feelings for Emeraldas, and performs engineering feats like rebuilding radios from salvaged parts. These iterations highlight his adaptability across timelines while preserving his technical prowess and steadfast friendships.