Kyouhei Yamaguchi

In the world of Sougo Tokiwa and Sento Kiryu, their "companions" are losing their memories one after the other as they're replaced by other people. The Super Time Jacker, Tid , appears before them. He orders his powerful underlings, Another Double and Another Den-O, to pursue a young boy called Shingo. While fighting to protect Shingo, Sougo meets Ataru, a young man who loves Riders, but Ataru says that Kamen Riders aren't real. What is the meaning of those words? While the mystery deepens, the true enemy that Sougo and Sento must defeat appears in the Kuriogatake mountain...

Kamen Rider 4 is a web series which was released as an accompanying special to the film Super Hero Taisen GP: Kamen Rider 3. It introduced a new rider, Kamen Rider 4, who is the fourth Kamen Rider cyborg created by Shocker after Kamen Riders 1, 2, and 3. The plot goes around a time loop created by the Shocker that resets whenever someone dies, but whenever the loop resets Shocker itself somehow grows stronger and stronger. Thus, it is up to the Riders to decide whether to keep on fighting a useless battle... Or end the loops for good by sacrificing one of their own.