Stunts
A história começa seguindo a batalha de Ex-Aid e Para-DX contra Build durante Kamen Rider Ex-Aid: True Ending. Build aparece e tira os poderes da Ex-Aid, mas Sento não se lembra de que esse incidente acontece, pensa que é um sonho. Misora fez dois novos Fullbottles. Quando Sento chega a um lugar chamado de Smash, ele encontra um Nebula Bugster, a última mutação do vírus Bugster. Enquanto Sento luta contra o Nebula Buster, Ryuga é exilado em uma realidade alternativa, onde a parede do Sky Wall existiu, onde conheceu o Emu e os Gamer Riders. Os riders do mundo de Build e os riders do mundo de Ex-Aid, ao lado dos lendários Riders: Fourze, OOO, Gaim e Ghost enfrentarão essa ameaça!
Yukio Hara
Terumi has no memory of her life leading up to when she nearly drowned as a child in her town's local lake, Lake Shoryu. Terumi has been supported by her family and her close childhood friend Yukio since that time, although her family also does not seem to understand the reason for this childhood incident. 12 years later, Terumi finally decides to leave her town for a new job, but before doing so, begins investigating the drowning incident together with Yukio in order to know the truth. During her investigations, Terumi meets a man named Soda, who seems to have the same experience of nearly drowning and recovering with no memory as she does. As she digs deeper, a strange relationship between her and the legend of Lake Shoryu begins to surface.
