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?

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.