Summary
In March 1945, American bombers destroy most of Kobe during the waning days of the Pacific War. Seita and his sister Setsuko, children of an Imperial Japanese Navy captain, survive, but their mother dies. She is cremated in a mass grave outside and Seita is seen carrying a small wooden box containing her ashes. Seita conceals their mother's death from Setsuko. The siblings move in with an aunt. He hides his mother's box of ashes in the garden. Seita retrieves a supply cache he buried before the bombing and gives everything to his aunt, save for a tin of Sakuma drops, which he gives to Setsuko. The aunt convinces Seita to sell his mother's silk kimonos for rice, which devastates Setsuko.
As rations dwindle, the aunt becomes resentful of the children as Seita does nothing to earn the food she prepares for them. At her suggestion, Seita withdraws some money from his mother's bank account to buy a charcoal stove and other supplies. Following an air raid, the siblings move into an abandoned bomb shelter. Among the belongings is the wooden box of his mother’s ashes. They capture fireflies from the marshes and release them into the refuge for light. The following morning the fireflies have died. Setsuko buries them and reveals their aunt told her their mother died, then tearfully asks why the fireflies had to die so soon.
The situation becomes dire when they run out of rice. A friendly farmer recommends that Seita swallow his pride and return to his aunt, but he refuses, instead stealing crops from farms and breaking into homes during air raids. A farmer catches him and brings him to the police station, but the sympathetic policeman lets him go.
Setsuko falls ill, and a doctor explains she is suffering from malnutrition. Seita withdraws the last of the money from their mother's bank account. He is distraught to learn that Japan has surrendered and that his father is most likely dead, as most of Japan's naval fleet have been sunk. Seita returns to Setsuko with food and finds her hallucinating. She dies as Seita finishes preparing the food. Seita cremates Setsuko's body and her doll in a straw casket. He carries her ashes in the candy tin along with his father's photograph.
Seita dies of starvation a few weeks later at a Sannomiya train station surrounded by other malnourished people. A janitor, tasked with removing the bodies before the Americans' arrival, sorts through Seita's possessions. He finds the candy tin and throws it into a field. Setsuko's ashes spread out, and her spirit springs from the container and is joined by Seita's spirit and a cloud of fireflies. The two board a ghostly train and, throughout the journey, look back at the events leading to Seita's death as silent, passive observers. Their spirits, healthy and content, arrive at their destination: a hilltop bench overlooking present-day Kobe, surrounded by fireflies.
Source: Wikipedia (CC BY-SA 3.0)
