- The story begins following Ex-Aid and Para-DX's battle against Build during Kamen Rider Ex-Aid: True Ending. Build appeared and took Ex-Aid's powers away, but Sento has no recollection of such incident happening other than a dream. Misora has made two new Fullbottles.
When Sento arrived to a Smash distress call, he found a Nebula Bugster instead, the latest mutation of the Bugster Virus. While Sento battled the Nebula Buster, Ryuga was blown into an alternate reality where the Sky Wall never existed, where he meets Emu and the Gamer Riders. The Riders from the world of Build and the Riders from the world of Ex-Aid, alongside the Legend Riders Fourze, OOO, Gaim, and Ghost will stand up against this threat!