Agito Makishima is a third-year high school student whose appearance suggests an older age and who possesses a medium, muscular build. His parents' company was bankrupted by his uncle, Genzo Makishima, leading to their suicide. Genzo, a high-ranking Chronos Corporation member, adopted Agito but treated him only as an employee, fueling deep-seated resentment and a desire for revenge. This past forged Agito into a shrewd, calculating individual who masks his true intentions and prioritizes survival by strategically proving his usefulness within Chronos. Through his position in Chronos Japan, Agito acquired extensive knowledge of the organization's operations, including Zoanoid optimization and the Guyver Units. He orchestrated the theft of three Guyver Units by manipulating a Test Type Zoanoid. After an explosion scattered the units, he secured the third one, bonding with it to become Guyver III while concealing this affiliation from Chronos leadership. He manipulated events from the shadows, directing Chronos's retrieval efforts towards Sho Fukamachi (Guyver I) to observe their tactics and the Guyver's capabilities. He deliberately did not intervene when Genzo (transformed into the Zoanoid Enzyme) killed Sho, anticipating the control medal could regenerate the host—a theory proven correct when Guyver I resurrected. Agito's Guyver III identity was exposed to Chronos when he declared himself "Zeus" during the destruction of the Chronos Japan branch—a symbolic statement of his intent to overthrow the organization, mirroring the myth where Zeus usurped his father Cronus. This forced him into open conflict. He later rescued Sho's friends, Mizuki and Tetsuro Segawa, during their abduction by Chronos, intertwining his path with Sho's while maintaining his own agenda. Though allied with Sho against Chronos, Agito consistently viewed him as a pawn, believing Sho's reluctance to endanger innocents and perceived naivety made him inferior as both a person and a Guyver user. Following Chronos's global takeover (X-Day), Agito survived the destruction of the Creator ship at Relic's Point and surfaced in Canada. There, he founded and led the resistance movement "Zeus' Thunderbolts," using his Guyver abilities for strategic strikes against Chronos facilities. His rivalry with Sho intensified, particularly over the Guyver Gigantic armor. Agito wrested control of the armor (dubbed "Gigantic Dark") from Sho through willpower, believing its power wasted on Sho. However, Sho later reclaimed permanent control during a battle, prompting Agito to seek a method to create his own Gigantic armor, requiring access to control mechanisms within a Creator ship beneath Chronos headquarters. Agito exhibits a cold, ruthless personality, rarely letting sentiment influence his decisions. He demonstrates a willingness to endanger civilians or sacrifice allies to achieve his goals, contrasting Sho's protective nature. He harbors a strong sense of superiority, believing himself the rightful wielder of ultimate power. Despite this detachment, he maintains a close, complex bond with his childhood friend and loyal retainer, Shizu Onuma, who willingly transformed into a proto-zoalord (Griselda) to advance his ambitions. As Guyver III, Agito possesses all standard Guyver abilities: enhanced strength, speed, and durability; dual high-frequency blades on each forearm; a head laser; gravity control for flight and graviton attacks; regenerative capabilities tied to the control medal; the Megasmasher particle cannon; and environmental adaptability. The armor's appearance under his control features a distinct black color scheme and more menacing design elements, possibly reflecting his personality. Functionally identical to other Guyver units, effectiveness depends on the host's combat skill and tactical mindset. Agito's strategic acumen and aggressive fighting style make him a formidable user.