One night, high school student Sho Fukamachi discovers a mysterious metal object. Then in a blinding flash of light, Sho finds that he has accidentally fused with the Guyver, a mecha of mysterious alien design. Now, to save his girlfriend, Mizuki Segawa, along with the entire world, Sho must become the Guyver to fight the Chronos Corporation and their biocreatures, called Zoanoids, who are hell-bent on world domination.

At a run down school the "Ultimate Teacher" Ganpachi is sent to get things back on track and prepare the delinquent students for the real world. But the students don't want Ganpachi ruining the gang they got going so their boss, Hinako, fights back Ganpachi aided by her secret power...her lucky kitty underwear. Things get more interesting when we findout Ganpachi is the result of genetic experiments.