Masato Kusaka is the principal user of the Kaixa Gear and the sole individual capable of transforming into Kamen Rider Kaixa in the alternate world depicted in the film. In this reality, the organization Smart Brain has nearly wiped out humanity, leaving only a small remnant of survivors confined to a refugee camp called Paradise. Kusaka operates as a fighter for the Human Liberation Army, a resistance group that opposes Smart Brain's dominion. He is the only member of the resistance who can engage Orphnochs directly and effectively, making him a vital combat asset. Over time, however, he has grown cynical and disillusioned with the resistance's cause. He no longer listens to the words of Mari Sonoda, the symbolic hope of the human survivors, and instead acts in a self-serving manner, contributing to the overall despair and lack of direction within the group. His personality in this story is marked by detachment and selfishness, a departure from more complex portrayals in other narratives. When Smart Brain launches a major assault on Paradise, Kusaka confronts the powerful Kamen Rider Psyga. Despite his combat abilities, he is quickly outmatched and killed in the battle. His death underscores the overwhelming might of Smart Brain's forces and the desperate situation facing humanity. As Kamen Rider Kaixa, Kusaka wields the Kaixa Driver and the Kaixa Phone to initiate his transformation. The Kaixa suit generates a higher output of Photon Blood compared to Kamen Rider Faiz, granting him superior physical power at the cost of reduced speed. His weapons include the Kaixa Shot, a knuckle-duster that delivers a high-impact punch called the Grand Impact; the Kaixa Pointer, which attaches to his leg to execute a diving kick known as the Gold Smash; and the Kaixa Blaygun, a versatile firearm that can also deploy a blade for slashing attacks. He also has access to the Side Basshar, a sidecar motorcycle that can convert into a bipedal battle machine. Kusaka's role in the story is brief but significant: his defeat and death early in the film establish the high stakes and the formidable threat that the resistance must overcome, setting the stage for the return of the missing rider believed to be humanity's last hope.