|Name: Jun Shibaura|
|Designation: Kamen Rider Gai|
|Weapons: Metal Horn, Guard, Metal Visor|
|Advent Cards: Final Vent, Confine Vest, Strike Vent, Metalgelas|
|Contract Beast: Metalgelas|
|Jun was an arrogant and annoying 21 year-old college computer programmer who liked toying with others and took the Rider War all like a game. He is a 3rd year college student at Meirin University, extremely well-versed in computers and programming to be in the Matrix Netgame Club. He is the son of a company president. He joined the Rider war simply to be the winner of the Rider war. Jun even used his Matrix members' thrill-seeking urge against them to fight to the death in a game similar to the Rider war while he watched from the shadows. Investigating the matter, Shinji meets Jun and loses his Dragreder card to him when attacked. He used both Shinji's card and the virus he uploaded to the ORE Journal mainframe to blackmail himself into their head of their company. Shimada eventually managed to wipe out his programming with her own virus, while Miyuki/Raia stole back the Dragreder card. Soon after, Jun was picked up by the police for his ties to the Matrix member murders, getting his father to bail him out with Kitaoka/Zolda's aid.
Jun even went so far as to reveal the true identity of the other Riders among them, impressed with Asakura/Ohja's sadistic nature. To suit that end, Jun kidnapped Yui to start a "Rider party" between him, Knight, Raia, and Ryuki. However, in the middle of the fight, their battle gets intertwined with the one between Kamen Rider Zolda and Kamen Rider Ohja, who used Gai a shield to take the blunt of Zolda's Final Vent before killing him with his own hands. After dying, his monster Metalgelas was loose and was tamed by Ohja. In the 13 Riders TV Special, Jun also spat in Shinji's ordeal to end the Rider War, which he and his college friends laughed to. He was also some of the conspirators started by Verde to trap Shinji in a "truce" between the fighters. Later he and the remaining fighters fought Ren and Shinji as Knight and Ryuki respectively to finish them off. Later after Ren dies with Shinji mourning by his side, Gai while away from the big fight with mirror monsters, went to finish Shinji after his Ryuki deck was destroyed by Odin, but was consumed by the mirror monster Death Spider.
Gai's attack methods usually involve his Confine Vent card to cancel any weapons from the other Riders while using the Metal Visor on his left-shoulder to conjure his Metal Horn gauntlet as well as summoning his contract monster Metalgelas to fight alongside him and execute his Heavy Pressure Final Vent, carried by his Contact Monster as a lance, with the Metal Horn extended in front of him to pierce through the opponent.