Since his grandfather Yasuji died, Kousuke Kumagaya has drifted away from his once‑close companion Natsume Tonai. Their friendship, once unbreakable, now feels fragile. The two had grown up side by side in the same apartment block, almost like siblings, but now they clash because Natsume clings to memories that Kousuke has let go of. The divide deepens when they learn the old complex will soon be torn down.
Rumors of a ghost haunting the abandoned building lure Kousuke"s friends to drag him to the demolition site. There he discovers Natsume standing nearby, and a quarrel erupts over an old camera that once belonged to Yasuji. Natsume snatches it and rushes toward the roof, but as she teeters on its edge a violent storm pours down, flooding the structure.
The children are now adrift at sea with their apartment block as a makeshift vessel. Cut off from the outside world, Natsume and Kousuke must set aside their differences if they hope to navigate back home.
