Ryuga Dogai is a Makai Knight who holds the title of Golden Knight Garo and has overcome many trials and tribulations. Tonight, he will both summon the armor of Garo and cut down man-eating monsters, Horrors. Then, Koyori, a Makai Priestess, showed up. In order to receive the aid of the Golden Knight, she informs him of the urgent situation that is shaking the world. "The Gate of Destruction will be opened." "The Gate of Destruction" is the oldest gate where Horrors are said to have first appeared in the Human Realm. For some reason, it is on the verge of opening again. Guided by Koyori, Ryuga visits Creacity, a city with a hidden gate. In the city where the scent of darkness leaking from Gate of Destruction prevades, Ryuga senses evil and immediately engages a Horror. In the midst of a fierce battle, a mysterious Makai Knight suddenly appears. The Knight is Souma Shirahane, clad in "Hagane" Armor. What is the fate of Souma, who hunts Horrors as a titleless Knight Hagane!? Will Ryuga be able to stop the opening of The Gate of Destruction!? Now, a fierce story that approaches the origin of "The Protector" begins.