Jak Xamma, originally named Jack Hanma, is the Canadian-born son of Yuujirou Hanma and Diane Neil, a Canadian UN operative. He was conceived when Yuujirou raped Diane during the Vietnam War. Learning of this trauma in childhood ignited his obsessive drive to surpass Yuujirou through extreme, near-fatal training regimens, often exceeding 12 hours without rest and causing severe muscle deterioration. Discovered training in a church at age 10 by Father Samuel, the priest became a paternal figure supporting him. When conventional methods failed, he accepted experimental X-4 steroids from Dr. John, enhancing his physical capabilities at the cost of mental instability, addiction, and a drastically reduced lifespan. His physique transformed from 193 cm (6'4") and 116 kg (255 lbs) to 243 cm (8'0") and 211 kg (465 lbs) via multiple limb-lengthening surgeries by Dr. Kureha Shinogi. Key traits include blonde hair, blue eyes, extensive training scars, and later titanium dentures after losing teeth in combat. He adopted the ring name "Jack Hammer" for the Maximum Tournament in the Underground Arena to hide his identity. Before his first match, he flirted with Kozue Matsumoto, provoking his half-brother Baki Hanma. His tournament fights demonstrated overwhelming dominance: defeating Sergio Silva with an uppercut, overpowering Kengo Misaki, and advancing past Alexander Gallen. His quarter-final victory against Gouki Shibukawa involved countering Aiki techniques through biting, though Shibukawa noted Jack's average intelligence outside combat. He lost the finals to Baki, with fleeting demonic imagery appearing on his back during the match. Yuujirou confronted him about steroid use during the event, nearly provoking a duel. His fighting style initially combined pit fighting and brute force amplified by steroids. After losses to Pickle (where half his face was bitten off) and Izou Motobe (who shattered his teeth), he developed "Goudou," a discipline centered on biting techniques, marking increased tactical maturity. His personality is defined by relentless determination and sacrificing longevity for strength. Early portrayals show instability, animalistic behavior, and singular focus on revenge, but post-defeats reveal greater composure, humility, and calm activities like feeding koi fish with Tokugawa. Underlying complexity exists: he views Baki as a rival yet harbors genuine care, and while he despises Yuujirou, he acknowledges their biological tie. His backstory includes killing a polar bear with brutal efficiency, mirroring Yuujirou's feat. Post-tournament developments involve recovering from a coma after the Pickle fight and undergoing further surgeries. His moral compass prioritizes vengeance above all, explicitly stating readiness to "exchange the strongest body ever for death" to defeat Yuujirou.