Satanos was once an ordinary man who reincarnated as the strongest Demon King, the final boss of a game-like world. He discovers a grim truth: if he is ever defeated, the entire world will come to an end. And if the hero dies, the world resets to the hero’s last checkpoint. Unwilling to rule and longing for a free life, Satanos fakes his own death in front of the hero. From the shadows, he secretly begins protecting the heroes, as the true threats aren't just demons but also corrupt nobles and self-serving individuals plotting against them. Thus begins the carefree life of a former Demon King, now living in an adventurer city surrounded by eccentric characters who end up becoming his unsuspecting “shadow heroes.”