The film is based on a 1967 semi-autobiographical short story by .
To understand the weight of the film, one must understand its origins. Author Akiyuki Nosaka lived through the firebombing of Kobe in 1945. He lost his adoptive father, and crucially, his younger sister, Keiko, died of malnutrition—a fate he blamed himself for, believing he should have been able to save her. He wrote the story as a personal act of penance. Grave of the Fireflies-Hotaru no haka
Setsuko was his little sister. She was six, with a laugh like wind chimes and a habit of catching fireflies in the summer. After the bombing, they had moved into an abandoned shelter by the river—a damp, earthen burrow that smelled of rot and mosquitoes. Kenji had promised he would protect her. The film is based on a 1967 semi-autobiographical