The announcement features three Kamen Rider logos: the 1971 Kamen Rider logo, the Kamen Rider Den-O logo, and the Kamen Rider Ex-Aid logo. In the background is the Kamen Rider Den-O BGM.
It then cuts to Kamen Riders Ex-Aid, Brave, and Snipe fighting Riders in a "game space". We get to see Snipe vs. Faiz, Stronger and Decade, Brave vs. Specter, Gaim and Drive, Ex-Aid vs. Rider 1, and Mach and Kuuga. After the other riders are defeated, Den-O attacks Ex-Aid, and then they start working together. The video ends with Momotaros announcing the movie.
Take note, 2017 marks the 10th anniversary of Kamen Rider Den-O, and the last time Kamen Rider Den-O was heavily involved in a Kamen Rider production was in the OOO, Den-O, All Riders: Let's Go Kamen Riders film back in 2011.
[Source: Kamen Rider Facebook]