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.

Once upon a time, in the land of Fenarinarsa, there was a king and a queen and they had a little girl named Momo. Momo's royal parents told her that in order to govern Fenarinarsa wisely she would have to learn as much as she could about people, and the best place to do that was on Earth. Once on Earth, Momo discovers an island with a secret garden where everyone is a child. In the garden she meets Peter who controls the fountain of youth which keeps everyone young. Together Momo and Peter learn the importance of following their dreams as they fight to keep the power of the fountain of youth from getting in the hands of an evil organization.