In a world that never noticed him, Sayan lived a life of quiet despair—overworked, betrayed by his wife and best friend, abandoned by fortune, and finally claimed by terminal illness, dying alone in an empty apartment with no one to mourn him.But death was not the end.Reborn in a brutal fantasy world as a helpless infant, Sayan carries the memories of his broken past. Once again, he starts at the bottom—weak, talentless, mocked as a failure. Yet on the brink of his second death, deep within a monster-infested dungeon, an ancient voice awakens within him.He is the reincarnation of the long-defeated Demon King.A dark system ignites. Shadows bend to his will. Every kill fuels explosive growth. Fallen enemies rise as his eternal shadow army.No party. No allies. No trust.This time, Sayan will rise alone—unstoppable, unforgiving, and cloaked in darkness—as the Shadow Sovereign whose name the world will never dare forget.A dark isekai tale of betrayal, rebirth, and overwhelming vengeance. Inspired by Solo Leveling, with a protagonist who starts as the ultimate underdog and becomes an overpowered lone ruler of shadows.