Synopsis
After the death of his grandfather Yasuji, Kousuke Kumagaya has drifted apart from his childhood friend Natsume Tonai. Raised like siblings in the same apartment building, the two are now at odds because Natsume clings to the past, and the news that their old complex is set for demolition only widens the divide. Hearing a rumor that a ghost haunts the abandoned building, Kousuke's friends pull him into the demolition site to investigate. When Kousuke finds Natsume there as well, they argue over an old camera that once belonged to Yasuji. Natsume grabs it and runs off, but just as she is about to fall from the rooftop, a heavy rainstorm suddenly engulfs the entire building, flooding the ground around it. Now the children are drifting at sea with the apartment complex as their ship. Cut off from the outside world, Natsume and Kousuke must resolve their differences if they hope to find a way back home.
Background
The apartment complex where the film is set is modeled after the original designs of the Hibarigaoka Danchi, which was one of the largest housing complexes in Tokyo during its time.