So it has
been revealed that the new Gaim Gaiden will be 'Kamen Rider Gridon VS Bravo.'
Yes, that's right, the acorn boy with the hammer and the pastry chef are back. Don't worry, they've already promised that characters we might actually care about, such as Takatora (Zangetsu) and Kouta (Gaim) will also appear. Apparently the member of Kamen Rider Girls who wore the Sengoku Driver back in the day is still in the band, and therefore will be making an appearance too.
It appears that both Gridon and Bravo will be getting new forms. If you look closely in the trailer, Takatora (Zangetsu) is shown holding his version of the Kachidoki (Triumph) Arms Lockseed, which has only previously appeared in the stage show dedicated to him and briefly cameoed in the movie 'Kamen Rider Zio: Over Quartzer.'
The special is being directed by Satoshi Marota (a secondary director on Gaim) and written by Nobuhiro Mouri (also a secondary writer on the show).
The theme tune for the special is called "You are the HERO" and is sung by 'Shock Eye', who is a member of the band 'Shonen no Kaze' who performed the original show's theme tune (under the name 'Gaim no Kaze').
This two part special is being released on Toei's Tokusatsu Fan Club streaming service. The first part is available now (!) and the second part will be released on November 1st.