Birth of the 10th! Kamen Riders All Together!!

Birth of the 10th Kamen Riders All Together, Jg Tanj Kamen Raid Zenin Shg? is a Kamen Rider Series Japanese TV special that aired on January 3, 1984. It is a special meant to celebrate the birth of Kamen Rider ZX, the 10th person to don the Kamen Rider title.

After being shown a video detailing the history of Kamen Ridersto Super1, Ryo was amazed that there were others like him. He then joins the Kamen Riders in raiding the base. However, during the raid he encounters his former comrade, Mikage, who forced him to fight as Tigeroid. After being forced to kill his friend, ZX joined the Kamen Riders as they battled not only Ambassador Darkness and the Combat Roids, but also monsters from previous Rider Nemesis organizations. When Ambassador Darkness used the Space Break System on the Kamen Riders, they synced their powers with ZX, using his ZX Kick to kill Ambassador Darkness and destroy Badans base even as its Great Leader appeared and bid the Riders farewell. Soon after, ZX joined the ranks of the Kamen Riders as their 10th member.The Badan Empire , Badan Teikoku? claims to be the successor of all previous groups that attempted to conquer the world but fell without fulfilling that ambition. In Kamen Rider Spirits, several references infer that the Badan Empire was actually created by an alien entity, and supported terrorist groups starting with Shocker secretly working towards bringing the true form of their leader to Earth. The Badan later resurface during the events of Ressha Sentai ToQger vs. Kamen Rider Gaim Spring Break Combined Special and Heisei Riders vs. Shwa Riders Kamen Rider Taisen feat. Super Sentai ........

Source: Wikipedia