Diend's World
Junichi Kaito / Kamen Rider Glaive
Junichi Kaito is Daiki's older brother within his home world, known as the Diend World. Like Daiki, Junichi is also a Kamen Rider, Kamen Rider Glaive, setting up the operation to overthrow Fourteen. However, Junichi was actually a double agent who worked to flush out the last two Kamen Riders of their world until Daiki unknowingly captured him, and as a result, played the role as Fourteen's puppet right hand in charge of the area management committee. However, once Fourteen is destroyed, freeing everyone else from the brainwashing, Junichi reveals the truth with intent to be the next Fourteen. In spite of not being able to kill Daiki, with Tsukasa affirming he still has his free will, Junichi considers his brother dead to him and leaves.
Haruka Miwa / Kamen Rider Larc
Haruka Miwa is a young woman who resists Fourteen as Kamen Rider Larc in the Diend World, she is a friend of Daiki's. She took part in the operation to overthrow Fourteen and ended up escaping with Shin when the operation was a failure. Since then, she has been on the run from Fourteen's minions. She helps fill Tsukasa in on what is currently happening in her world.
Shin Magaki / Kamen Rider Lance
Shin Magaki is a hot-blooded young man who resists Fourteen as Kamen Rider Lance in the Diend World. After the operation to overthrow Fourteen failed due to Daiki's efforts, he escaped with Haruka. He holds a grudge against Daiki for selling out his older brother but eventually forgives him.

Jashin 14 is leader of the Roaches and ruler of the Diend World, assuming the human-like form of Fourteen for his "ideal peace", turning humans into mindless slaves. He is a massive creature with multiple arms that floats through the air. He is destroyed by Decade in Complete Form with aid from Armed Hibiki, cutting him in half. After his demise, the Roaches vanish and everyone he'd brainwashed were set free.
Bossroach is one of the Roach enforcers who watch over the human race, whom he sees to be inferior. Bossroach resembles the Caucasus Undead. Bossroach is then destroyed by Decade Complete Form using the Emperor Final KamenRide.
Darkroaches are Category Unknown Undead who are minions of Fourteen in the Diend World, going after any one who breaks the law. Many of them are killed by the Riders and when their master is destroyed by Decade and Armed Hibiki, the Darkroaches fade away into nothingness.
Series:  Kamen Rider Decade