Grand Beast Rei is second-in-command of the Ashu. Furious Demon God Gai and Hyouga freed this powerful tiger-like demon from the 100-Demon Mirror by using the captured Natsuki's blood as sacrifice.
Rei is a calm, yet vicious and calculating demon who loves to make people suffer. He has power over fire and can breath forth an illusion-filled miasma that preys on the self-doubt of his victims. Satoru tried to use the Dual Crusher Mixer Head on Rei, but Rei simply broke out of it with his fire powers.
GoGo Sentai BoukengerThough defeated by Satoru Akashi wielding the Crossbow of Fighters, and terminated by Ultimate DaiBouken and the Ashu Spirit Extinguishing, Arch Priest Gajah revived him as Quester Rei. In this form, Rei wields a sword that also turns into a gun and can also shoot lighting from his hands. He also kept his Ashu ability to project a person's memories and thoughts. He was able to put Natsuki into a trance that made her believe that her purpose as the last of the Lemurians was to bring destruction to the future humanity.
After the defeat of Homunculus he was finally destroyed by the Boukengers with the Dual Crusher in Task 42.
His name comes from the Japanese word for spirit. While his Ashu form was based on Gosei Sentai Dairanger's Mythical Chi Warrior Won Tiger, his Quester form is modeled after Kibadaioh.
Unfortunately, he revived again with Gai in Kamen Rider × Super Sentai: Super Hero Taisen together with the other villains of the past Super Sentai and Dai-Zangyack Great Commander. He is seen fighting HououRanger, then Kamen Rider ZX, GoseiRed, HurricaneBlue and HurricaneYellow during the final battle.