Granute, secret lifeforms, kidnap humans for "Dark Market Snacks." Shoma, from another world, transforms with Gochizo, a sweet-eating monster, into Kamen Rider Gavv via a mouth-like belt to stop Granute's attacks and save people.

A mysterious man arrives in a quiet Japanese town. With him, he carries a strange helmet that allows one to re-experience the happiest moment of their life. He goes on to make the village people recall their happy pasts, but his face is lined with worry and a sadness that deepens. What is the secret of this helmet? And what is he trying to do with it?