Half a year ago, Yun-jae Kim lost his wife and daughter in a car accident, and lives in despair day after day. One evening, his diary completely erases itself, leaving behind an ominous message: "you can see them again". 'The 'Holy Grail' is given to those who overcome the 'game' of 'The World of the Backside', and it is said that if you use it, you can reunite with your lost family ... In the cruel world where only the strongest survives, Yun-jae becomes the only one who knows the future. Will he be able to fulfill his wishes?