In the final battle against the Demon Emperor Solemus, humanity's greatest hero, Gron, sacrificed his life to save the world. Five years later, he awakens in the enemy camp, reborn as a low-tier demon minion. To his shock, a remnant of the Demon Emperor survives inside his new body. Refusing to despair, Gron decides to harness this dark essence and use it to his own advantage. No longer bound by his past, the former hero walks a bloody path to settle the war forever.