Kikaider(from the Kikaider Reboot movie) guest stars in an upcoming episode of Kamen rider Gaim and fights alongside Gaim against Hakaider.

And here is the synopsis of the team-up that came from a magazine scan that was translated by Nihon Hero:

"Jiro (Kikaider) from Kikaider Reboot is seen walking with his guitar in the streets of Zawame City where a crack opens and Yagi (Goat) Inves makes his appearance before him. Yagi Inves rampages in the city attacking many civilians. It's up to kikaider to save the city when Kamen Rider Gaim is nowhere to be found. While Kikaider fights Yagi Ives, Hakaider makes his appearance. Kota transforms into Kamen Rider Gaim and fights Hakaider. Hakaider performs his Hakaider Shot at Gaim Orange Arms with his gun. So Kamen Rider Gaim Orange Arms transform into Kamen RIder Gaim Kachidoki Arms to show Hakaider the power of his DJ Gun. Yagi Inves later teams up with Hakaider in an attempt to defeat Kikaider and Kamen Rider Gaim."

This team was also similar to the team-up between the Go-busters and Space Sheriff Gavan Type G in order to promote an upcoming movie.

Credits to the Henshin Justice team for this great news!