Adel (アデル Aderu) is Alain's older brother who is the second highest authority in the Gamma World. Adel is rather heavily influenced by his father's plan to create a perfect world but hardly ever receive any recognition from him, causing Adel to silently planned a takeover from his father's position. Alongside Igor, he is directly responsible for the Gamma forces' invasion on the human world, suggesting it in hopes for compensating the defects in Edith's machine, which transfers the Gamma World population souls to Eyecons. The reason behind his recent madness was ever since his beloved mother died, which involves on killing Takeru's father, Ryū, after a traitorous ghost hunter, Chikara Saionji defect to Gamma's force for using Daigo Fukami's children, Makoto and Kanon as a guinea pig, trapping them inside Gamma's world for ten years.

Adel begins his move for first destroying the Eyecon body of his father Adonis to render him mortal, imprisoning him while framing Alain for their father's "assassination" while destroying his younger brother's Eyecon body. Adel soon has the Gammisers under his command, killing Adonis for real while Takeru and Alain were looking for Makoto. Having merged with the Gammisers, Adel begins to harvest the power of the Great Eye but was halted by Edith as Gamma Ultima Ebony, who believed that Adel's actions will endanger the Gamma World's citizens despite the young emperor has no regard for it. After being defeated by Ghost Mugen Damashii and the number of Gammisers reduced to 3 (Electric, Time and Oscillation), Adel "realized" his "errors" that the utopia he imagined cannot be created, but instead chooses to become one with the world. His first step is to destroy his own Gamma body by smashing the Eyecon it used to create, much to Alia's horror. By the time he used himself as a backup plan to activate Demia, Makoto had outright states Adel that his insufferable god-like delusions perfectly made him despised by many, Alia and now later Gyro felt the same way about Adel's unforgivable actions, turning everyone including his own people on Gamma world into his personal slaves. After Takeru and Alia connected with him, Adel realised the error of his ways and finally saw his father for the actual person he is, as well as revealing that the reason he killed Takeru's father, Ryū is due to his jealousy. During this moment, the Gammisers, whom had been manipulating Adel from beginning, possessed him for his connections to the Great Eye before Takeru was forced to killed Adel under his own wish. Before departing to the afterlife, Adel thanked Takeru for saving him, prayed for the future of his siblings and warned them not to follow the same mistake he did.

As a member of the Gamma royal family, Adel possesses a special Gamma Eyecon that allows him to transform into a Gamma Ultima form. As a Gamma Ultima, his strength exceeds that of a Gamma Superior, and he can disable projectile weapons and melt things by simply touching them. Once Adel merges with the remaining Gammisers, he transforms into the Perfect Gammiser (パーフェクト・ガンマイザー Pāfekuto Ganmaizā), a form that equals Ghost's Grateful and Mugen Damashii's powers with the ability to project plant vine-like tentacles.

Adel is portrayed by Akihiro Mayama (真山 明大 Mayama Akihiro). As a child, Adel is portrayed by Saion Ebizuka (海老塚 幸穏 Ebizuka Saion).

Series:  Kamen Rider Ghost