The social worker who had been working overtime for 27 days in a row encountered the "upside-down moon" on the last subway train during the rainy season. The door opened, and the unfamiliar line "Lin-13" dragged him into the 27 circulating carriages; each section had a skeleton and a flower from the other side. He holds the "Book of Erosion of Bones" and must collect 27 bones before the train is completely eroded in order to find the only way back - but he doesn't know that the last bone is actually his own.
