This OVA loosely adapts the opening four chapters of the Guyver manga, covering the same core storyline: the origin of the Guyver, the clash with Vamore, the battle against Guyver 2, and the debut of Guyver 3. The key changes involve swapping Tetsuro out for Mizuki, and replacing Lisker with a female operative named Valcuria, which consequently makes Guyver 2 female as well. The story also explores Sho's inner turmoil as he struggles to cope with his transformation, including a harrowing scene where his friends are executed in cold blood.
One night, high school student Sho Fukamachi comes across a strange metallic object. In a sudden blinding flash, he discovers he has inadvertently bonded with the Guyver, a mecha of mysterious alien design.
Now, to protect his girlfriend Mizuki Segawa and the entire world, Sho must take on the role of the Guyver and battle the Chronos Corporation and their bio-engineered creatures, the Zoanoids, who are determined to conquer the globe.