Yu Amanai transitioned from serving as a U.S. Presidential bodyguard to becoming a fighter recruited by Yujiro Hanma for the Maximum Tournament. This 30-year-old man of Japanese and American heritage stands 188 cm tall (6'2") and weighs 89 kg (196 lbs), possessing a tall, slim build with long legs and a characteristically blank, emotionless stare. Amanai displays a distinct duality in personality. Outside combat, he presents a friendly demeanor and expresses distaste for unnecessary violence. Within a fight, however, he becomes ruthlessly unpredictable, exemplified by his relentless kicking of Minoru Yamamoto's face without regard for his life, halted only by judges. Conversely, he expressed urgent concern for Doppo Orochi's injuries during their match, repeatedly calling for officials to stop the fight, reflecting deep respect. He developed his unique Amanai-ryū Martial Arts, emphasizing acrobatic jumping techniques to sustain extended airborne movement. This style integrates hypermobility, self-momentum control, and grappling. His combat philosophy centers on understanding an opponent's emotions and desires, which he attributes to "love" rather than aggression. A key technique is the "No-Motion Jump," propelling him upward with minimal telegraphing for unexpected aerial attacks. Amanai possesses superhuman strength, speed, and durability, though documented capabilities range between City Level (7-B) to Small Building Level (9-A) for attack potency and durability, noting his feat of breaking Doppo Orochi's leg. Speed assessments similarly vary from High Hypersonic+ to Supersonic tiers, while lifting strength estimates span Class 100 (90+ metric tons) to Class 5. He utilizes analytical prediction, anticipating opponent moves by discerning what they "want least," alongside enhanced senses that allowed him to detect threats faster than fellow bodyguards. His Maximum Tournament participation saw a first-round victory against Minoru Yamamoto showcasing aerial assaults. In his second-round match against Doppo Orochi, Amanai employed complex acrobatic evasions and mid-air strikes. The brutal fight culminated in Amanai fracturing his own skull in three places and dislocating his jaw, yet he continued fighting until Yujiro Hanma intervened. This battle highlighted both his tenacity and unexpected compassion towards Orochi. No significant post-tournament appearances, character development, or involvement in spin-offs/media beyond the Maximum Tournament Saga are documented.