Originally constructed from a human body for hazardous radioactive labor in nuclear power plants, Robotomi 560SEL-Mark. II ("Robo") required cybernetic modifications to survive these conditions. Following a crushed revolt against inhumane treatment, he volunteers as a gladiatorial combatant beneath The Cape, driven by vengeance against humanity for his suffering—a backstory embodying forced dehumanization and exploitation.

In the arena, his reinforced metal exoskeleton grants superhuman durability. During a forced duel with Riki-Oh, Riki-Oh acknowledges Robotomi’s inherent humanity, challenging his worldview. This pivotal moment shifts Robotomi’s focus from indiscriminate revenge to specifically targeting General Washizaki, architect of the cyborgs’ oppression. Robotomi’s physical design differs slightly between media; his OVA depiction features a more metallic mouth structure and vulnerability to impalement by arena spikes—a susceptibility exploited when Riki-Oh telekinetically impales him with levitated structures.

Surviving these injuries, Robotomi evolves from a vengeant fighter to recognizing solidarity with Riki-Oh. He aids Riki-Oh against Washizaki before making his final charge at Washizaki’s observation booth. Declaring his humanity, Robotomi is bisected by Washizaki’s sword, concluding his arc from dehumanized laborer to defiant martyr.