Kyoichiro Kuroi (黒井 響一郎 Kuroi Kyōichirō) is a man who was kidnapped by Shocker and turned into Kamen Rider 3 (仮面ライダー3号 Kamen Raidā Sangō), a Kamen Rider that should have never existed, and who drives a car called the TriCyclone (トライサイクロン Torai Saikuron). Prior to being kidnapped by Shocker, Kyoichiro was once a race car driver who sought to win anything he can. Through a History Modification Machine (歴史改変マシン Rekishi Kaihen Mashin), surviving members of the Shocker organization kidnapped Kyoichiro and converted him into a cyborg before sending him back in time to defeat the Double Riders. Without Kyoichiro knowing, just in case if he regained his consciousness back, Shocker also turned him into a vessel of Rider Robo (ライダーロボ Raida Robo) for the Great Leader. Prior to carrying out his mission, Kyoichiro is sent to test his skill against Go Shijima during the events of Shuriken Sentai Ninninger vs. Kamen Rider Drive: Spring Break Combined 1 Hour Special and spares the Kamen Rider as he is not the one he is after. Kyoichiro is then sent back in time to the year 1972, defeating the Double Riders after they defeated the Gel-Shocker organization. This causes time to be altered, with a restored Shocker becoming a world power with only a few Kamen Riders remaining, namely Yuto Sakurai (Kamen Rider Zeronos), Go, and Takumi Inui (Kamen Rider Faiz), who together attempted to save the Double Riders upon discovering that their history has been corrupted. In this new time line, Kyoichiro finds himself on the run from both Shocker and some Kamen Rider resistance groups before Shinnosuke, Yuto, and Go try to find a way clear Kyoichiro's name and change history back to normal. He is targeted by the Kamen Riders (known as Shocker Riders in that timeline), even Kamen Rider Faiz who is only after him to restore the world to normal. Kamen Rider 3 is later re-brainwashed while sacrificing his life to have Kamen Rider Zeronos escape first. It is ultimately revealed that Kyoichiro was not brainwashed, and his role as a rogue Kamen Rider was just a mere ruse that he wanted to become the strongest Kamen Rider and used Shocker to feed his obsession of defeating all of Kamen Riders endlessly. However, he still does not yet realize that he is still being used by Shocker itself, as a vessel for the Great Leader's use to modify history via the Rider Robo. The following day, he and his Shocker goons find Yuto and capture him. However, he is confronted Shinnosuke, who has his memories of history restored to normal. He who challenges Kyoichiro to a race on the next day, which he accepts but only if he can keep both Yuto and Kiriko Shijima hostage. During the race, Kamen Rider 3 uses the TriCyclone's weapons and Shocker Riders (including Mashin Chaser) as shield to win for Shocker. However, his dirty tricks are counteracted by Drive's remaining allies, including Kotaro Minami as Kamen Rider Black RX, Kamen Rider Faiz, and Kamen Rider Mach. Kamen Rider Drive tries to tell Kamen Rider 3 that he should try to win without any dirty tricks, because racing with his actual skills instead of cheating makes him a winner in his heart regardless of winning or losing the real race, and asks if Kamen Rider 3 regrets killing the original Double Riders prior the timeline alteration in the past. Kamen Rider 3 refuses and says the deaths do not matter, as long he vows to become the strongest Kamen Rider there is, but he loses the race in the end. He ultimately accepts his loss as a sign of good sportsmanship, realizing his error. However, the Great Leader uses him to activate Rider Robo to attack the surviving Kamen Riders and those who defied Shocker. With the last of his own willpower, Kyoichiro sends the original Double Kamen Riders to the future to restore the Shocker Riders' memories to normal. He breaks free of the Great Leader's control and helps the other Kamen Riders fight Shocker, while Kamen Rider Drive and the Shuriken Sentai Ninninger team destroy the Great Leader's Rider Robo form, which Kyoichiro realizes is the source of his own Kamen Rider powers. Before the timeline returns to normal, Kyoichiro bids his Kamen Rider allies a farewell, but promises that he will meet them in the restored timeline, where he is a human once more and supported in his racing endeavors by the Tachibana Racing Club and BOARD.
Kyoichiro Kuroi is portrayed by Mitsuhiro Oikawa (及川 光博 Oikawa Mitsuhiro).