Kang Jihan dies after three years of fighting monsters that destroyed humanity. His final regret is failing to protect his younger sister, Sora. Then he wakes up ten years in the past. The apocalypse has not begun, and Jihan remembers everything about the future. With his knowledge, he plans to prepare for the coming disaster and save the people he lost. But a mysterious system suddenly appears. Instead of recognizing him as a hero, the corrupted system classifies him as the Final Boss. His skills are incomplete, his quests are broken, and even the system does not understand its own abilities. Jihan decides to use it anyway. He has already died once. This time, he will become strong enough to protect everyone, even if humanity eventually sees him as an enemy. But when Jihan activates his first corrupted skill, the timeline changes. The apocalypse begins 347 days earlier than expected. Now, Jihan must survive a future he no longer knows.