Kaisei Mogami

is the main antagonist of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Riders. He was created from the fusion of two multiversal counterparts of , who wished to destroy both the World of Kamen Rider and the World of Build using his Enigma.
==History==
Eventually, both Mogamis would finally meet as the Engima was fully bridged both of their worlds, fusing into Bikaiser. However, Kamen Rider Build would join forces with the Kamen Riders from Ex-Aid's world to put a end to Bikaiser's megalomaniacal schemes and perishes from Build Rabbit Tank Sparkling and Ex-Aid Muteki Gamer's Rider Kicks.
==Fusion Components==
Kaisei Mogami.png|Kaisei Mogami (World of Build)
Kaisei Mogami Ex-Aid World.jpg|Kaisei Mogami (World of Ex-Aid)
 
==Forms==