Shoma, who comes from a different world, is saved by a boy named Hajime when he collapses from hunger. Shoma excitedly eats the snacks that Hajime gave him, but as soon as he does, Gochizo are born one after another.

Meanwhile, freelance writer Hanto is gathering information on the appearance of "monsters" while doing research.

Hajime hides Shoma in his secret base and hurries home when a mysterious man appears before him. The man transforms into the monster Granute and approaches Hajime.

Shoma tries to save Hajime, but he is no match for the Granute. Gochizo suddenly appear in front of the suffering Shoma. Shoma sets and eats the Gochizo! He transforms into Kamen Rider Gavv and confronts the Granute!