The Grou Dragon (グラウ竜, Gurau Ryū?) is the guardian of the Barankas fruit which it produces within its body. The Grou Dragon is a sentient mechanical dragon created by the Makai to reside inside the Crimson Forest and hunt the Horrors there. He has a main dragon head on the top and four sides to his body (almost cube-like). His cube-like body has a rustic color and when he speaks he rotates it to a different side of his body. Whenever he reacts to some thought his body makes a turn. Two sides of his body have a white naked woman statue, the front side a white gothic skull of a creature, and the back side with just gears that resemble the yin/yang sign. The Grou Dragon has a blaster-cannon, his statues are actually large mechanical claws, his gothic skull is actually a claw and grinder, and his gear side has multiple mechanical tentacles. He has four mechanical legs and his back is capable of bringing out two large wings for flight.
His only purpose is to destroy Horrors, but when he encountered Kouga he was curious about Kouga's nature to protect people. He challenged Kouga to a fight to examine his need to protect (save Kaoru) and offered him the Barankas Fruit as a victory prize if Kouga could defeat him with all his strength. The Grou Dragon helped Kouga summon his armor and his rider Gouten to fight it at his full potential while engaging in a clash of ideals if saving lives is more important than destroying Horrors. Kouga almost lost to him, but Zero stepped in to assist him. Kouga thought he lost the fight because he had help, but the Grou Dragon said that if Rei lend his power to Kouga, that's also part of his power. The Grou Dragon then vanished and Silva remarked that the Grou Dragon was never alive and that the power of the Makai will eventually recreate it.
The Grou Dragon is voiced by Masakazu Handa (半田 雅和, Handa Masakazu?).