Reviewer Jesuotaku observed that the fireflies at the end at the same color as the lights of the city Kobe. These fireflies have little time of their lives, and Kobe would later be devastated by an earthquake...
Which would make this Harsher in Hindsight (relatively speaking), as the film came out in 1988 while the Great Hanshin Earthquake struck in 1995.
When Setsuko buries the fireflies, she asks Seita ‘Why must fireflies die so young?’ while burying them. Most viewers thinking this would be the explanation for the title would be missing its true meaning. The children are the fireflies, and their impromptu home has allures similar to a tomb. ‘Grave of the Fireflies’.
Ya know, since the aunt was asking how come Seita and Setsuko don’t find other relatives, how do we know those relatives are even alive? I mean, after all, Tokyo did get bombed about the time or a little after those two had to live with their aunt, so unknowingly and basically, she was sending them there to die.