If anyone's curious, the original Kamen Rider, while being a single continuous "season," ran for nearly 2 years (98 episodes) and went through a number of different phases. It started out as a fairly dark, horror-tinged series about a man named Takeshi Hongo who was turned into a cyborg monster by the evil organization Shocker, escaping with his mind intact, and using his monstrous powers to fight and kill other monsters, while lamenting that he could no longer let himself become close to other people for fear of hurting them with the superhuman strength he couldn't control. Then, about 10 episodes in, the lead actor hurt himself badly doing a stunt, and the next 3 episodes were written around him, focusing on the supporting cast or on Kamen Rider in full costume, while introducing a new supporting character, Taki, to carry the action. He was supposedly an FBI agent, even though the FBI is a strictly domestic agency and should have no authority in Japan.
But starting with episode 14, they introduced a whole new lead, Hayato Ichimonji, who just showed up out of the blue and explained he'd been turned into a second Kamen Rider and saved by Hongo off-camera, and would now be taking over the fight against Shocker in Japan while Hongo fought them overseas. This was a soft reboot, with the mentor Tachibana changing his restaurant to a riding club, which gained a number of female members who became the new supporting cast, and were actually pretty bold and liberated and effective in fights, at least initially. They also introduced the "Henshin!" transformation call and ritual arm movements that became standard for Kamen Riders from then on. But they dropped the darker elements and character drama and went more for straight action, with Ichimonji being a much blander lead than Hongo. Taki stuck around, though, the first replacement hero becoming the sidekick to the second one.
They kept making changes about every 13 episodes, with the first onscreen Shocker general showing up around half a year in and getting replaced by the next one 13 episodes later, and so on. Hongo came back intermittently to fight alongside Ichimonji, and eventually he took over again entirely for about the last year of the series, inheriting Taki as his sidekick, with Ichimonji making only a few return appearances. Eventually Shocker got upgraded into another evil organization called Gel-Shocker, but not much changed aside from the design of their lair set (always the same set even though each identical lair was destroyed by Kamen Rider in pretty much every episode). Female cast members came and went, becoming mostly interchangeable and existing only to look nice and get routinely taken hostage, with only one lasting all the way through and being reduced from a kickass karate student to a helpless damsel in distress.
All in all, it started out kind of interesting (but very very weird) but soon settled into repetitive blandness.
