Set in the final days of World War II, Grave of the Fireflies follows Seita and his young sister Setsuko as they struggle to survive after the firebombing of Kobe. Their mother dies in the attack, a truth Seita initially hides from Setsuko to protect her. Orphaned and displaced, the siblings find temporary shelter with a distant aunt, but tensions grow as food becomes scarce and resentment festers. Eventually, Seita and Setsuko leave to live in an abandoned bomb shelter, finding brief comfort in the glow of fireflies they release at night.

As their situation worsens, Seita resorts to theft to feed them, but it's not enough. Setsuko grows weaker from malnutrition, and Seita learns that the war has ended and their father is likely dead. He returns to find Setsuko dying, and she passes away soon after. Heartbroken, Seita cremates her and keeps her ashes in a candy tin.

A few weeks later, Seita too dies of starvation. Their spirits reunite, watching over modern-day Kobe in peace. This haunting tale is a poignant reflection on the tragic cost of war and the fragile innocence of childhood.