Eight Kirino was a boy who seemingly lacked emotions and was disinterested in most things. A genius programmer, his only hobby was working on the Chou Super Hero Taisen game.
Eight was later hospitalized due to a fatal heart disease and had Hiiro Kagami assigned as his surgeon. However, when Hiiro asked him if he wanted to have surgery done, Eight expressed indifference towards it, leading Hiiro to not perform the surgery as he only cured patients who wanted to be cured. Right before he died, Eight transferred his essence into the Game World and into his Chou Super Hero Taisen game. Though Hiiro did not show it, this incident led him to feel guilty for not saving Eight's life.
Eight later created a Game World counterpart of Hiiro Kagami from real world Hiiro's regret for not saving a child. Seeking to make up for his real world counterpart's failure, Game World Hiiro unleashed enemies from the retro game Xevious upon the real world to destroy it so the Game World would be all that was left and the only world.
Eight was later encountered by Emu Hojo after he entered the Game World to participate in Chou Super Hero Taisen and obtain the powers of the Goriders to defeat the Game World enemies. Eight watched Emu and the other competitors in the Chou Super Hero Taisen tournament as they fought to decide who would become the Goriders.
Team Ex-Aid won the match and obtained the ability to become Goriders however, this also triggered the "Chou Shocker Taisen" bonus stage of the game, unleashing the Shocker forces that had been hiding out in the Game World upon the real world to destroy it. It was then that Eight and Another Hiiro reveal their true colors to the Kamen Riders and Super Sentai, announcing their plans to destroy the real world so the Game World would be the only world left.
As Ex-Aid, his Game World allies and the Kyurangers fight against the Shocker army, Naga Ray and Amu attempt to reason with Eight, but Eight remains emotionless and unaffected by Another Hiiro's plans. Eventually, after defeating Kamen Rider True Brave, the real Hiiro Kagami shows up and severs the connection between the Game World and real world, undoing all the damage that the enemies unleashed from it caused and leaving Eight seemingly trapped in the Game World while he and the others return to the real world.
However, Eight later manages to make it to real world, with Hiiro revealing that he left just enough essence for Eight to be able to return, though he could never go back. Eight was not concerned as he could still interact with his friends from the Game World through his Genm portable console.