|Name: Ryu Terui|
|Designation: Kamen Rider Accel|
|Weapons: Engine Blade|
|Gear: Accel Driver|
|Ryu Terui is a superintendent appointed to the Futo Police Department's Paranormal Crime Investigation Division, and is Jinno and Makura's superior. Prior to arriving in Futo, Ryu lost his family when they were murdered by a Dopant with a Gaia Memory symbolized by the letter W, driving him to seek revenge against this man. The mysterious woman known only as Shroud assists him, providing him with the Accel Memory, Engine Blade, and Accel Driver. He also develops a hatred for the city of Futo, seeing it as a gathering place of all kinds of scum. Prior to his series debut, Ryu makes a cameo appearance in a post-credits scene in Kamen Rider × Kamen Rider W & Decade: Movie War 2010 proclaiming that Kamen Rider Double is not the only Kamen Rider in Futo. From then, Ryu watches Shotaro and Philip from afar before formally introducing himself to them just as Shroud provides him with the Accel Driver. Though he and Shotaro clash at first, Ryu becomes an ally to the Narumi Detective Agency when it comes to investigating the Dopant crime wave, as well as picking up some of Shotaro's habits in dealing with Dopants even after losing it upon finally finding his family's killer: the Weather Dopant Shinkuro Isaka.
After obtaining the Trial Memory from Shroud and learning to use it, Ryu is able to finally take his revenge on the Weather Dopant, using the Trial Maximum Drive to destroy his Gaia Memory, after which Isaka dissolved as a result of his long term abuse of Gaia Memories. After Isaka's death, Ryu becomes more open to the others and continues his role as a Kamen Rider to fight off the Dopant crime wave prior to learning that it was Shroud who gave Isaka the Weather Memory, though she had no idea that his family would suffer as a result. Furthermore, Ryu learns he has a unique physiology, enabling him to withstand the intense power of certain Gaia Memories and was selected by Shroud because he can resist the Terror Dopant's Terror Field. Because of this, Shroud wants him to assume Shotaro's place as Double using his hatred to enable Double to reach full power. However, Ryu has shown Shroud that he can fight with compassion and does not need to be Double to fight. Furthermore, after Philip's disappearance after Jun Kazu's defeat, Ryu had grown to love Futo with a desire to protect it, overall a complete turnabout from his initial personality.
Ryu Terui transforms into Kamen Rider Accel through the use of Gaia Memories. However, Accel only has access to a single, default form with which he fights through the use of the Accel Memory which he inserts into the Accel Driver. Like Double and Skull, Accel can perform Maximum Drive finishing attacks which are necessary to destroy a Dopant's Gaia Memory in a Memory Break. Accel's standard Maximum Drive is the Accel Glanzer Rider Kick, after charging up power to a point where Accel's body is engulfed in orange flames, he executes a jumping spinning heel kick which releases energy in the form of tread marks. While armed with the Engine Blade, Kamen Rider Accel has additional Maximum Drives. Ryu tends to say "Let's break away!" whenever he assumes his Rider forms and states "Despair awaits you (all) at the finish!" and "[0.1-9.9] seconds, that is the time left until your despair!" upon executing a Maximum Drive attack.