Mason Park, a "Barbarian" bioengineered for space exploration, is sent back in time from a decimated 28th century to find hope for humanity. He lands in a war-torn Seoul where monsters roam freely and the remnants of society cling to survival through the Player System, a program that empowers soldiers with monster cores. Gifted with extraordinary strength, regenerative abilities, and the advanced technology of his time, Mason becomes a beacon of hope against the monstrous threats. He joins the Holy Knights, a band of players dedicated to selfless service, and quickly rises to prominence. However, Mason's idealism clashes with the reality of human conflict as he gets caught in the struggle between the benevolent but struggling Holy Knights and the ambitious, power-hungry Heavenly King Yekaterina who controls the Player System. Torn between the conflicting ideologies, Mason forms his own raid team, the Revengers, determined to carve his own path. He faces increasingly powerful monsters, including the Lich and the Ghost Dragon, battling not only for humanity's survival but also for his own sanity as he grapples with the darkness within him. His past trauma and his monstrous strength threaten to consume him, but he finds solace and support in the Healer Eun Yuri and the enigmatic Seo Yeonhee, both women drawn to his unique power and burdened by their own past. As Mason's fame grows and the world's eyes turn to him, he faces a choice: to be a tool of power used by others, or to be a symbol of hope that transcends human limitations and unites humanity against a common enemy. His journey is one of self-discovery, where he confronts the complexities of human nature and the meaning of true heroism in a world teetering on the edge of oblivion.