Let the experiment begin 2: Heroes reunited

After the defeat of Evolto, Kamen Rider Build and Cross-Z, Akira Kiryu and Ryuken Geki lived in the fused world. That is until Killabus the brother of Evolto erased the memories of Akira and the only thing he has is a rabbit. It's up to Ryu to help Akira regain his memories and for the two to reunite team build once more

Akira: "I'll hop my way towards for my memories and to bring back everyone I knew."