Kamen Rider is a fiction and action series by the Japanese genius Tokusatsu, created by Shotaro Ishinomori; this famous series dating back to nineteen seventy was originally created as a television series, which in fact has more than thirty seasons and one thousand four hundred and fifty chapters to its credit; its vertiginous success allowed the creation of more than eight films.
The followers of this old television series are very strict with the plots, and that is why generally all seasons are different and handle different arguments; like the spin-offs; however, this film starts at the end of the last chapter of the season entitled Build.
This new tape called Kamen Rider Build New World: Kamen Rider Grease; it is the second installment of the New World saga; which is based on the character of Kazumi Sawatari; a young man who inherited the responsibility of representing the Rokers of Hokuto and who tirelessly fights Evolto.
Simon Marcus, a high representative of the United Nations, who leads a subversive group that calls itself Downfall, whose sole intention is to sow terror to take over the entire world.
A day like any other, young Kazumi watches as his friend Misora works, this young man is madly in love with her; it takes courage and asks them to go out together, to which she answers affirmatively; excited Kazumi puts on her best clothes and buys a detail for the pretty girl; nevertheless the intentions of the lady are very different from those of the young; she simply wants some advice and company to buy a gift from her father, news that leaves Kazumi very sad.
Meanwhile, at the headquarters of the United Nations, Undersecretaries Taizan and Gentoku, meet with the high representative Simón Marcus, in order to discuss security and prevention strategies in case of a new terrorist attack. Gentoku accompanies Simon Marcus to the laboratory where he and scientist Katsuragi work on the recovery of the Build Rider.
At that time they are ambushed by members of the Downfall subversive group, who have the help of infiltrated security officers; Keiji Uraga is identified as the leader of the clan; Gentoku Himuro has no choice but to show his alter ego and take the form of the Kamen Rider Rogue to escape, but not before taking the Build Rider.
But Simon Marcus does not intend to allow it so he reveals his true identity as Phantom Crusher, and proclaims himself the absolute leader of Downfall; immediately he attacks the Rider Rogue, who falls defeated and with serious injuries, when he returns to his Gentoku form, Phantom shoots him and liquidates him, taking over the Build Rider.
Later, Misora is ambushed in her work and captured by the members of Donwfall, who take her with Phantom to be able to attract Kazumi, who after her amorous disappointment took a raft and fled to a desolate island off the coast of Hokuto.
The entire Downfall leader's plan goes according to his plans; already in his power the Build Rider and with the capture of the young Misora a battle with the Kamen Rider Grease is ensured; with the power of the three crows of Hokuto he will try how to stop the plans of Simon Marcus.