Will humanity inherit the heavens? Or the Worms?

20 years after the events of the series, humans and Worms are walking towards the path of coexistence. However, ZECT is secretly developing a new Masked Rider System. Yui Kagami, the son of Arata Kagami/Kamen Rider Gatack is qualified to use the new system. Arata Kagami also investigates a ZECT conspiracy all by himself, but a shadow of an unexpected person appears before him...!