At night, the escort girl Muduo and the writer Mianshan stroll in the People's Park. Mianshan tells of a novel he dedicated to his fiancée, which takes place after the end of the world, where a boy travels through an abandoned aquarium to rescue a dying mermaid. As the story progresses, the park seems to gradually become isolated from the world, and Mianshan searches for an exit back to reality, while the clues seem to be hidden in the experiences that Muduo shares with his fiancée.