Aptom began as a member of the experimental Zoanoid group known as the Lost Numbers, created by the Chronos Corporation after failing standard optimization. His initial designation was a battle creature designed to hunt other Zoanoids. Operating under Chronos command alongside comrades Somlum and Dyme, they faced contempt from standard and Hyper Zoanoids. This treatment fostered deep bitterness toward Chronos. The deaths of Somlum and Dyme during a confrontation with Guyver I solidified his personal vendetta against Sho Fukamachi, the host. Severely injured in that battle, Dr. Hamilcar Barcas subjected him to extensive reprocessing and experimentation. These procedures unexpectedly granted immunity to Zoalord telepathic control and significantly enhanced his innate abilities. He gained the capacity to absorb DNA from other Zoanoids, replicating their forms, powers, and combining multiple attributes into hybrid configurations. His regenerative capabilities became near-absolute, enabling recovery from minimal residual tissue. He also developed the ability to create clones possessing independent consciousness. His human form consistently appears as a muscular Caucasian man with slick black hair and a prominent vertical scar down the left side of his face, a result of his initial optimization. This form typically wears a leather jacket, jeans, and sunglasses. Driven by vengeance after his enhancements, he tracked Sho Fukamachi. He exploited Sho's psychological trauma to force a confrontation, taking Mizuki Segawa hostage to provoke Guyver I's transformation. During their battle, he showcased composite forms merging abilities from Zoanoids like Gregole, Vamore, and Enzyme II. Though seemingly destroyed by Guyver I's Mega-Smasher, his severed arm regenerated. He then ambushed and absorbed the Hyper Zoanoid Elegen, declaring independence from Chronos and intent to hunt other Hyper Zoanoids like Gaster. His rebellion led him to target higher-ranking Chronos figures, including Zoalord Richard Guyot. An encounter with Chronos founder Archanfel resulted in near-total disintegration, but he regenerated using fallen Zoanoid biomass and created clones to infiltrate Chronos's Relics Point base. Inside, he absorbed Gaster and used deception to infect Derzerb, creating a powerful composite form combining Elegen, Gaster, and Derzerb's abilities. He engaged ZX-Tole in a protracted battle, absorbing part of ZX-Tole's leg to acquire his powers before the base's destruction forced his retreat. After Chronos's global takeover on X-Day, he resurfaced in Tokyo. He monitored and protected Sho's allies, believing their safety would draw Sho out for their unresolved conflict. He eliminated Zoanoids surveilling the group, inadvertently alerting Chronos to his presence. Later, he faced an upgraded ZX-Tole, now a Lost Number equipped with countermeasures like a regeneration-inhibiting virus. During this battle, Sho intervened as Guyver Gigantic, saving him and the others. He regenerated using a defeated Zoanoid and reiterated his unresolved score with Sho before departing. His motivations gradually evolved. While vengeance against Sho initially defined him, prolonged reflection on Chronos's role in his suffering and the loss of his comrades led him to question this pursuit. He consciously chose to aid Sho and his allies against Chronos, particularly during conflicts involving Archanfel-possessed Masaki Murakami. Despite never considering Sho a friend, his actions aligned with resistance efforts. Chronos developed specific countermeasures against him, including Enzyme III to resist cellular absorption and attempts to exert control through implanted Zoalord cells.