On 21 September 1945, shortly after the end of World War II, a teenage boy, Seita, dies of starvation in a Kobe train station. A janitor sorts through his possessions and finds a candy tin, which he throws into a field. The spirit of Seita's younger sister, Setsuko, springs from the tin and is joined by Seita's spirit and a cloud of fireflies. They board a train.