In a world where dungeons suddenly appeared and skilled players compete for supremacy, a young man named Kanazaki Yukari dreams of conquering the ultimate challenge, the Luluhart Dungeon. However, he is branded as incompetent due to having no skills and is unable to even enter a dungeon. One day, a Dungeon Break occurs, unleashing monsters into the world. During the chaos, he rescues a gravely injured girl, who turns out to be none other than Demon Lord Luluhart. As gratitude, she grants him a chance to save the world by sending him back in time with her power. Now, six years in the past, Yukari must use his newly awakened Return by Death ability to challenge fate and fight to save the world!