In a world where dungeons have emerged in modern times and skilled players compete for dominance, a young man named Kanzaki Yukari dreams of conquering the ultimate challenge—the "Luluhart Dungeon." However, branded as "Skill-less" and deemed incompetent, he isn't even allowed to enter a dungeon. One day, a Dungeon Break occurs, unleashing monsters into the world. Amid the chaos, Yukari rescues a gravely injured girl—unaware that she is the Demon King Luluhart herself. In gratitude, she grants him a chance to save the world—by bestowing upon him the ability to return to the past using her power. Now, sent six years back in time, Yukari must harness the power of Return by Death and fight to change the world's fate!