Kamen Rider Spirits is written and illustrated by Kenichi Muraeda and the series takes place after the events of Kamen Rider Super-1. The series initially follows what happened to the 9 Kamen Riders after their respective shows ended, tying up loose ends in the process, until finally, we are introduced to the 10th Kamen Rider, Kamen Rider ZX as he fights the evil Badan Empire and later, team up with the other Kamen Riders.
The follow up series on the other hand, Shin Kamen Rider Spirits is still ongoing when it comes to translation and serialization. You can read Kamen Rider Spirits by clicking the links found on the side. [READ IT HERE OR HERE]