Green Moss Beneath the Steps

The Crown Prince dies of illness and his soul falls into the Underworld, where he meets a young woman named Yun Yi. They comfort each other, and in the end, both return to the human world, though their memories have been mortgaged away. They meet again within the palace walls, but do not recognize each other. The Crown Prince spends eight years obsessively searching for her, while she is right beside him, having forgotten the past. How can a promise forgotten by the netherworld lead them to recover each other's names and faces amid the vast mortal world?