After the end of World War II, in Sannomiya Station, a boy named Seita dies of starvation. After Seita’s body is removed, a janitor digs throw through his belongings and finds a candy tin, which he throws away. Later on, the spirit of Seita’s sister (Setsuko) emerges from the tin that was thrown away and reconnects with Seita’s spirit with a cloud of fireflies.
Seita’s spirit then begins to narrate a story, including the final events of World War II. We get a flashback from where it all began from when Seito and Setsuko were still alive. In one incidence, we see a terrible period when they were caught up in bomblets and many people died.
They both become stranded and then decide to move and stay with their aunty who tells Setsuko to sell her mother’s Kimono’s for rice. Also Seita goes to get necessities he had buried before the bombing and gives them to his aunt but retains a tin of Sakuma fruit drops which become a centre of the movie
Situations become worse at their aunt’s home, and they decide to leave amidst chaos