Sho Fukamachi, a 17-year-old second-year student at Narisawa High School, initially focuses on academics and cherishes his close friendships, especially with classmate Tetsuro Segawa and Tetsuro's sister Mizuki. His ordinary life shatters when he and Tetsuro witness an explosion near Lake Narusawa and discover a mysterious organic device. Sho accidentally activates this device, identified as a Guyver Unit, which forcibly bonds with him, encasing him in bio-mechanical armor. This unconscious transformation into "Guyver I" horrifies Sho, who recoils at his armored form. The Guyver armor grants Sho superhuman strength, speed, agility, and durability. Integrated weapon systems include High-Frequency Blades extending from his forearms for cutting virtually any material; a Head Beam laser emitter above the Control Medal; Sensor Orbs providing enhanced electromagnetic and thermal sensing; a Gravity Control Orb enabling flight and gravitational attacks like the Pressure Cannon; a Sonic Buster emitting destabilizing sound waves; and the Mega-Smasher, a high-output particle beam fired from his chestplate. The Control Medal, embedded in the armor's forehead, regulates the unit and stores Sho's genetic data and memories. Its destruction kills the host as the armor consumes them; if intact, it enables rapid regeneration and even full body reconstruction from minimal DNA residue, granting functional immortality. This ability allows Sho to survive and regenerate after multiple fatal encounters. Sho's transformation marks him as a target for the secret organization Chronos (or Cronos), which seeks to recover the Guyver units. Chronos deploys genetically engineered Zoanoid monsters against him, escalating the threats he faces. Sho fights primarily to protect his friends and family from Chronos, driven by responsibility and guilt whenever his connection endangers them. His protective feelings for Mizuki and bond with Tetsuro, whose scientific knowledge aids him, are central motivations. He also forms uneasy alliances with other Guyver hosts, like strategically cunning Agito Makishima (Guyver III) and vengeful journalist Masaki Murakami. Sho endures significant trauma and loss. His father, Fumio Fukamachi, is captured by Chronos and transformed into the anti-Guyver Zoanoid Enzyme II. During their confrontation, Enzyme II rips out part of Sho's brain. The Guyver regenerates him but operates autonomously in a berserk state, killing Enzyme II. Witnessing his father's death at his own hands causes severe psychological trauma, temporarily suppressing his transformation ability. He later confronts this trauma after the renegade Zoanoid Aptom forces him to remember. Sho also suffers multiple deaths: killed by the original Enzyme Zoanoid (Genzo Makishima), who removes his Control Medal, causing consumption; later regenerated from DNA on the recovered medal. At Relic's Point, Chronos leader Archanfel reflects his Mega-Smasher blast, disintegrating him completely. His consciousness survives within a fragment of an alien Creator ship, reconstructing his body over a year within a chrysalis-like object. Emerging from the chrysalis, Sho returns to a world conquered by Chronos following their global takeover ("X-Day"). He now possesses the enhanced Guyver Gigantic form, significantly amplifying his existing powers and granting new abilities like an Electromagnetic Barrier and the vastly more powerful Giga Smasher. This form later evolves further into the Guyver Exceed, featuring increased size, altered coloration, and access to ultimate techniques like the Gravity Implosion, which generates a matter-absorbing pseudo-black hole. Sho's battles extend beyond personal protection to challenging the Chronos-controlled world order, fighting for global freedom against a society where Zoanoids are integrated into everyday life under Zoalords' mental control. Despite immense power and profound loss, his core motivation remains protecting others.