Kaisei Mogami is the main antagonist of the 2017 film Kamen Rider Heisei Generations FINAL: Build & Ex-Aid with Legend Riders. He is a scientist of Namba Heavy Industries Ltd. from the World of Build working alongside his alternate counterpart, a Foundation X researcher from the World of Ex-Aid, to destroy both dimensions by merging both of them together.

He was portrayed by Kenji Ohtsuki.



Kaisei Mogami originally worked at the Touto Institute of Advanced Matter Physics where he discovered the Bugster Virus inside the Skywall. Theorizing that it came from a parallel world, Kaisei began working on a dimension bridging machine called the Enigma alongside Takumi Katsuragi.

When the Touto government did not approve his budget for the project Kaisei sought backing from the weapons manufacturing company known as Namba Heavy Industries Ltd.. While working at the company, Kaisei also developed a form of the Bugster Virus infused with Nebula Gas and created the Kaiser system.

However, Katsuragi discovered that Kaisei intended to use the Enigma device not just to create a bridge between the two dimensions but to merge them together and destroy them. Thus, Katsuragi quit working on the project and sabotaged the Kaiser system.

Completing the Enigma

2 years later, Kaisei put the finishing touches on the Enigma and began initiating the final stages of his plan to become ruler of both dimensions alongside his Ex-Aid counterpart. He set his Nebula Bugsters loose in order to lure out Build so he could claim the Doctor and Game Fullbottles from him. He was pursued by Cross-Z, but Kaisei managed to send him to the World of Build using his Enigma device.

His Ex-Aid counterpart meanwhile also set the Nebula Bugsters loose in order to empower his own Enigma machine. He then activates the machine and brings the Build Earth to the World of Ex-Aid.

Eventually, Kaisei as Left Kaiser merged with Ex-Aid Kaisei as Right Kaiser to become Bi-Kaiser as the final step of his plan to become ruler of both worlds. However, his plan was foiled when Build activated the Enigma early, preventing it from being able to converge the worlds on time. Bikaiser was then defeated by Kamen Riders Build and Ex-Aid.



           EX-AID LOGO Villains

Executives: Gamedeus | Parado | Graphite Bugster | Lovelica Bugster | Black Parado
Minor Bugsters: Salty Bugster | Alhambra Bugster | Revol Bugster | Motors Bugster | Gatton Bugster | Vernier Bugster | Kaiden Bugster | Charlie Bugster

Genm Corp.
Masamune Dan | Kuroto Dan | Ren Amagasaki | Hiiro Kagami

Next Genome Institute
Dr. Pac-Man | Soji Kuruse | Kazuhige Ryuzaki | Ageha Takeda | Saiko Yaotome

Foundation X
King Dark's Hologram | Kaisei Mogami
Beast Rider Squad: Kamen Rider Ouja | Kamen Rider Tiger | Kamen Rider Sasword | Kamen Rider Dark Kiva | Kamen Rider Beast

Machina Vision
Johnny Maxima | Kagenari Nagumo | Ninja-Players

Totema | Shocker Greeed | Hiruchameleon | Experimental Wolf Man | Kani Laser | Tiger-Roid | Mogura-Roid | Yamaarashi-Roid | Suddendath Beta | Space Ikadevil | Space Spider Man | Urga | Buffal | Shocker Combatmen

Taiga Hanaya

           BUILD LOGO Villains

Night Rogue | Blood Stalk | Takumi Katsuragi | Nariaki Utsumi | Shingo Kuwata | Eita Kawai | Masahiro Nabeshima | Norio Matsui | Yoshikazu Takahashi | Shinobu Katsuragi | Faust Guardians

Yoshiko Tajimi | Blood Stalk | Kazumi Sawatari | Hokuto Three Crows | Akaba | Aoba | Kiba | Massugu Ubukata | Hokuto Guardians

Masakuni Mido | Kamen Rider Rogue | Fu Washio | Rai Washio | Seito Guardians | Hard Guardians

Namba Heavy Industries Ltd.
Juzaburo Namba | Nariaki Utsumi | Fu Washio | Rai Washio | Sawa Takigawa | Kaisei Mogami | Guardians | Hard Guardians

Blood Tribe
Killbus | Evolt | Kengo Ino | Ryoka Saiga | Mitsuomi Gohara

Needle Smash | Strong Smash | Burn Smash | Flying Smash | Press Smash | Ice Smash | Stretch Smash | Fang Smash

Simon Marcus | Keiji Uraga | Phantom Crushers | Guardians | Hard Guardians

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