One year after the battle days of Sword of Logos ended, Reika Shindai is preparing for her wedding. However, this happiness is unexpectedly abrupted when her brother Ryoga receives some disturbing details about the upcoming wedding.

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?