The Makai fight a secret war against the demon forces known as Horrors, evil creatures that manifest themselves through darkness to devour Humanity. On the frontlines are the Makai Knights, given the task of watching over a district and eliminating any Horrors that manifest there.

GARO follows the tales of the Knights bearing the title of ‘Golden Knight Garo’, and their duty to vanquish the Horrors and protect Humanity from the darkness.

Mendosa, the chief adviser of the king of Valiante, begins a campaign to hunt down "witches," resulting in the deaths of many magical knights and their sorcerer assistants. Anna, a sorceress married to the knight Herman Lewis, gives birth to a son before her execution. Herman takes their child, Leon, and flees, raising him to be the heir of the legendary Golden Armor. By the time Leon grows up, Valiante is completely in the control of Mendosa, who drives out Prince Alfonso and his mother. Alphonso decides to seek out the man who inherited the Golden Armor to reclaim the throne and save his people.

Makai Knight Jinga Mikage , along with his partner Makai Priest Fusa and younger brother Toma, hunts the beasts known as Horrors that are born from the human malevolence known as “Inga.”

Heian-kyō, capital and the center of elegant, aristocratic culture, is heavily guarded by a spiritual force field -- or so it seems. In reality, onmyōji (court magi who create the spiritual force field) can only defend the palace located in the northern part of the city; in downtown, monsters known as "horror" that feast upon human souls roam after sunset. There are, however, a group of heroes protecting commoners from "horrors" in darkness.