Superhero Senki Spoilers
The Kamen Rider-like entity which the Four Sages are going to transform into had also appeared in Superhero Senki. These were dubbed as Guards of Agastya Base and they were easily defeated by Asmodeus.
It is not yet known what they'll be called in the TV Series. Calling them as Agastya Guards in TV Series would make no sense.
As confirmed by CraneJoe a few months earlier, Hikounin Sentai Akibaranger's Gear appeared in Superhero Senki. Zenkaizer used this in a situation in the movie. Akiba Red asks for Zenkaizer's sign in the movie. The ability of this Sentai Gear is unique. It generates a Death Flag situation for the enemies.
By the way, Fuku Suzuki who plays Mysterious Boy in the movie had played young Nobuo Akagi (Akiba Red) in Akibaranger Season Tsuu.
As speculated earlier, Fuku Suzuki does play Shotaro Ishinomori. Shotaro Ishinomori becomes emotional after meeting Mei Sudo as if she resembles Shotaro Ishinomori's late sister.