The fireflies in this film in a way or another represent the war victims that died in honor and light .
A US military B-29 can be seen in the background of the movie poster. This represents the very person who is burned by an airstrike. The way it burns looks like the light of a firefly, and that light represents the soul of the victim.
The screenplay of Hotaru no haka [English: Grave of the Fireflies] was written by Japanese animated film director Isao Takahata, who also directed the movie. He based the story on a semi-autobiographical novel of the same name —『火垂るの墓』— by Japanese novelist Akiyuki Nōsaka, who lost his sister from malnutrition in 1945 wartime Japan.
The square wooden box that Seita carries with him contains his mother's ashes. Sadly, since it was a mass cremation, the ashes that Seita obtained are not, strictly speaking, "his mother's ashes". Rather, they are what may or may not contain some of her ashes.
