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.
Granute is an intelligent lifeform that operates secretly in the human world. They kidnap people in search of "Dark Market Snacks." People are being attacked one after another by Granute. Shoma, a young man from another world, rises up to save the people. Together with Gochizo, a small monster born from eating sweets, he transforms into Kamen Rider Gavv with a mouth-like belt.
