In the aftermath of a mysterious event two decades ago in Kanazawa prefecture, The Lost Ground emerged—a region where the earth fractured and rose to towering heights. Amid this desolate landscape resides Kazuma, a young mercenary eking out a living through odd jobs. Uniquely bestowed with the Alter ability, Kazuma can manifest a metallic alloy on his right arm and torso. His fateful encounter with HOLY, a faction dedicated to controlling Native Alter Users, sparks a fierce rivalry with Ryuho, a prominent member of the organization, setting the stage for an intense conflict.