The sandy city of Sagan was in dire straits due to an unusual outbreak of Horrors. Makai priestess Rian and Elmina save the residents of Sagan while eradicating the Horrors. Then, a gigantic horror named Zagdam, covered in waste, appeared and engaged Rian and the others in a fierce battle. In the middle of the battle, a mysterious Makai Knight suddenly appears. The knight turned his blade not only against the horror, but also against Rian. As the battle descends into utter chaos, Ryuga Dogai finally returns to Rian's side.

Ryuga Dogai entrusts Rian with the task of purifying the Garo armor. Ryuga heads to Yoroi-no-zuka, where the armors of fallen Makai Knights were enshrined, in search of the power to protect Sagan from Horrors. Then the Makai Priest Lector creeps up on them mysteriously... Meanwhile, Rian is informed by the dragon clan's Hiden that the time remaining for Ryume, the current Sentinel, is drawing to an end. Rian ponders the meaning of the words entrusted to her by Ryume.

Lector reveals a terrifying truth. Ryūga Dougai learns the true identity of the Horror attacking the town of Sagan, as well as Lector's motives. Meanwhile, Rian and Elmina are heading for the shrine. Elmina can't hide her irritation at Rian's conflicted thoughts: "Why did Ryume choose me to be the successor to the Sentinel?" At the same time, Sagan's elder Monma discovers that miraculous water is gushing from a well that was thought to have dried up.

Caught in Elmina's trap, Rian was sealed away in another world. In this eerie world, Rian is relentlessly assaulted by illusory trials. Meanwhile, in the parched town of Sagan, Ayura began recounting her past rescue by Lector to Ryuga Dougai. Then, the Makai Dragon that Rian released appears. Will Ryuga be able to rescue the captive Rian...?

Ryuga Dougai and Rian have returned from the other world. Rian, heading once more for the shrine, confided in Ryuga her resolve to confront her unknown roots. At that time, in the town of Sagan, Monma and Ayura were shouting with joy at the well that was filled to the brim with water. Meanwhile, a mysterious voice echoes in Elmina's mind as she stands in a daze after killing Hiden. An eerie water seeps into her feet...

Ryuga Dougai and Lector fight against the countless Sand Warriors that appear. Lector was suffering from pain in his petrified left arm as a result of the forbidden ritual he had once performed to save Ayura, the "Kyuin Houga Technique." Meanwhile, Rian returns to Sentinel hall, guided by Hiden's thoughts, only to find Elmina waiting there, intent on taking Ryume's life. As each battle descends into utter chaos, a golden light finally pierces the darkness of Sagan...! And then, the Sand King Horror Garzas also reveals himself.