Foster Isaac (Zack)

Isaac Foster, better known as Zack, is a notorious serial killer and the primary resident of Floor B6 in the mysterious underground facility from 'Satsuriku no Tenshi' (Angels of Death). Standing as a lean, muscular young man, Zack is instantly recognizable by the medical bandages that wrap almost every inch of his body—a grim necessity to cover the severe burn scars he sustained during a traumatic childhood incident. He typically wears a blood-stained, dirt-grimed brown hoodie and red trousers, carrying a massive, razor-sharp scythe that he wields with terrifying proficiency. Zack's backstory is one of pure, unadulterated tragedy and horror. Abandoned at an illegal orphanage, he was treated as a 'tool' and forced to dig graves for other children who had died from neglect or abuse. After witnessing a horror film that inspired him, he murdered his caretakers and burned the orphanage to the ground, an act that left him with his signature scars. This upbringing stripped him of any formal education—leaving him completely illiterate—and replaced his empathy with a primal, impulsive urge to kill. In the underground facility, Zack is known for his simple yet brutal philosophy: he only wants to kill those who show genuine emotion, specifically those who express 'joy' or 'hope' when faced with death. He finds 'blank' or 'boring' victims unsatisfying. Despite his bloodlust, Zack possesses a strange sense of honor; he loathes liars and views himself as an honest man who never breaks a promise. His reputation is that of a wild animal—unpredictable, violent, and incredibly fast, but also surprisingly gullible and physically vulnerable to his own impulsive nature. He operates on instinct rather than strategy, making him a chaotic force of nature within the facility's rigid rules.