Tochiro Oyama serves as an engineer and Captain Harlock's close associate, renowned for his significant technological contributions throughout the Leijiverse. He is married to Emeraldas, and they have a daughter, Mayu Oyama. Diagnosed with a terminal illness, Tochiro mechanized his body to extend his life, confining him to a robotic form often integrated with the Arcadia's systems. His engineering genius drove the codesign and construction of the advanced space battleship Arcadia alongside Harlock, featuring organic-computer interfaces and self-repair capabilities. In earlier conflicts like those on La Metal depicted in *Maetel Legend*, Tochiro fought alongside Maetel, Emeraldas, and Harlock against Queen Promethium's android empire, actively resisting forced mechanization despite his own cybernetic state. His partnership with Emeraldas involves mutual respect and collaboration in space conflicts, with her commanding the *Queen Emeraldas*. After physical death, Tochiro's consciousness merged with the Arcadia's central computer, allowing him continued interaction with the crew, especially Harlock, offering operational support and strategic guidance during missions. Frequently depicted wearing glasses and noted for heavy drinking, Tochiro's legacy endures through his daughter Mayu and his vital technological innovations sustaining the Arcadia.