Genos began as a 19-year-old human whose peaceful life ended when a rogue cyborg annihilated his hometown and family. Rescued while critically injured by Dr. Kuseno, a scientist tracking the same cyborg, Genos demanded transformation into a weaponized cyborg for vengeance and justice. Dr. Kuseno replaced most of his organic body with advanced cybernetics, forging Genos's core drives: hunting the "Mad Cyborg" responsible for his tragedy and pursuing absolute strength to prevent others from suffering similarly. After witnessing Saitama effortlessly defeat Mosquito Girl during a battle, Genos became his self-appointed disciple, determined to uncover the secret of Saitama's power. His appearance blends human-like artificial skin on his face and ears with a fully mechanical body, featuring spiky blond hair, black sclera with yellow irises, and pierced ears. Exposed mechanical components define his cybernetic limbs and joints, optimized for combat. Genos undergoes frequent body upgrades by Dr. Kuseno, leading to varied designs across story arcs. These include reinforced armor plating, integrated weapon ports, specialized arm units like "Arms Mode" for enhanced firepower, and facial framing during high-intensity combat. Personality-wise, Genos exhibits intense seriousness, discipline, and analytical thinking, rarely displaying humor. He meticulously records battles and strategies, reflecting his logical heroism approach. Initially prioritizing strength above all for revenge, he often charged into fights impulsively, suffering severe damage. Saitama's influence gradually softened his rigidity, fostering emotional growth, greater empathy, protectiveness towards civilians, and moments of introspection about concepts like "fun." Despite this evolution, his core traits endure: dedication to justice, deep reverence for Saitama, and loyalty to Dr. Kuseno. He displays open hostility towards those disrespecting Saitama or Dr. Kuseno and professional respect for heroes like Bang and Bomb. As the S-Class hero "Demon Cyborg" (Rank 14, later Rank 11), Genos wields extensive cybernetic abilities. His body grants superhuman strength capable of shattering cliffs and lifting vehicles, supersonic speed rivaling ninja like Speed-o'-Sound Sonic, and exceptional endurance due to his artificial form. He lacks conventional vulnerabilities like blood loss or pain receptors, though corrosive substances like acid pose a threat. Key combat systems encompass palm-mounted "Incineration Cannons" firing plasma blasts from controlled bursts to building-melting discharges like "Spiral Incineration Cannon" or "True Spiral Incineration Cannon." Other features include rocket boosters for flight and agility, hyper-sensors for environmental scanning, detachable limbs for tactical flexibility, and adhesive gel to immobilize fast opponents. His nuclear reactor power core doubles as a data recorder preserving information even if his body is destroyed. Weaknesses include over-reliance on frontal assaults, energy depletion in prolonged battles, and frequent post-combat repairs by Dr. Kuseno. Genos undergoes significant development across media. His combat capabilities evolve through technological upgrades like leg-mounted boosters enabling kinetic kicks ("Jet Drive Arrow") and shoulder-mounted lasers. He progresses from losing to Demon-level threats like Deep Sea King to strategically engaging Dragon-level monsters like Elder Centipede and the Psykos-Orochi fusion. His emotional arc shifts from cold detachment to nuanced humanity: expressing concern for civilians, processing grief after defeats, and demonstrating loyalty through actions like defending Saitama's reputation. During the Monster Association arc, his core records critical events after his body's destruction, revealing Saitama's emotional response to his apparent death, catalyzing deeper self-reflection about heroism beyond strength. Genos also pursues broader justice, investigating organizations like the Monster Association and suspicious S-Class heroes while continuing his quest for the Mad Cyborg. Relationships define key aspects of his journey. His bond with Saitama involves unwavering reverence, often interpreting Saitama's casual advice as profound wisdom. He documents Saitama's daily routines and defends him against critics, occasionally displaying jealousy towards others close to Saitama like King or Overgrown Rover. Dr. Kuseno serves as a father figure; Genos expresses gratitude for his cybernetic body and repairs but remains singularly focused on vengeance, sometimes straining their dynamic. Among heroes, he clashes with Speed-o'-Sound Sonic, respects senior figures like Bang, and dismisses the Hero Association's authority when it conflicts with his goals.