In a world teetering on destruction, humanity's only hope is becoming stronger in a mysterious tower offering four modes: easy, normal, hard, and the brutal "alone mode." Kang Taesan, despite choosing the easy route, becomes the most skilled player upon conquering the tower. But as doomsday nears, he realizes that he isn't strong enough to save Earth and turns back time, embracing "alone mode" to level up even more. With a second chance, can he amass enough power to prevent the end of the world?