Toei had announced the Theme Song Artist & the Title for Build NEW WORLD: Kamen Rider Grease. The title of the song is "Perfect Triumph" & performed by Masanori Kobayashi (WAЯROCK). He had commented that "Kazumi Sawatari / Kamen Rider Grease's strong feelings & the fire burning inside his Heart has been expressed in my song".
The new trailer for Build NEW WORLD: Kamen Rider Grease has revealed that Nariaki will be back as Mad Rogue. But it is not sure how he is able to transform back as he didn't have human experimentation on him to remember about the Old World.
Build NEW WORLD: Kamen Rider Grease will have a very special spin-off called "She said will get in relationship with Idol Otaku" (Original Japanese Title: ドルヲタ、推しと付き合うってよ / Doruota, oshi to tsukiautteyo). This will be screened along with Build NEW WORLD: Kamen Rider Grease.
Only the people who have been into Human Experimentation have resurrected their memories of the Old World in the Sento Kiryuu's (Kamen Rider Build) New World. In the New World there were people who are planning to rule the world using the power of science as a Weapon. Their name is Downfall. These are the terrorist group who are planning to make use of Rider System.
Build NEW WORLD: Kamen Rider Grease hasn't revealed a single supporting cast for the movie till now but yesterday Kaho Takada (Misora Isurugi) had posted some pics from the making of the movie where Kouhei Takeda (Kazumi Sawatari / Kamen Rider Grease) is seen teaching Kaho-chan Baseball. The post clearly mentions it to be from the filming of Kamen Rider Grease.