Renowned adventurer Adol “the Red” Christin and his companion Dogi arrive at Balduq, a city annexed by the Romun Empire, only for Adol to be detained before setting foot inside. While imprisoned, he meets a mysterious woman named Aprilis who turns him into a Monstrum, a being with supernatural Gifts and the power to exorcise monsters.

Now, Adol must ally with his fellow Monstrums to fend off the fearsome threats emerging from a shadowy dimension called the Grimwald Nox, as well as unravel the mysteries of the Monstrum curse, and the truth behind the unrest within Balduq.