Though the widespread popularity of many of Studio Ghibli’s films might cause you to believe otherwise, not every animated film is a colorful, light-hearted romp. Grave of the Fireflies in particular helps to dispel that popular belief; it released on April 16, 1988 (the same day as the very light-hearted My Neighbor Totoro, by the same studio) and aimed to show the cost of war.

Grave of the Fireflies follows two siblings, Seita and Setsuko, as they struggle to survive in the final months of World War II in Japan. After being caught in a bombing raid, the siblings lose their mother and are forced to move in with their aunt, who quickly becomes resentful of their presence when food rations begin to run low. Eventually, Seita and Setsuko leave their relatives and move into an abandoned bomb shelter. Though they release fireflies for light, Setsuko becomes distraught after the insects die.

The pair quickly runs out of food, and Seita resorts to stealing from local farmers so they can continue to survive. However, it’s not enough, as Setsuko becomes seriously ill from malnutrition. Though Seita does his best to save her, she dies shortly thereafter. When Seita learns of Japan’s surrender to the Allied Powers, he loses even more hope, as his father was part of the Imperial Japanese Navy, and Seita presumes he’s dead. Eventually, Seita too dies from malnutrition. The film later shows his and his sister’s spirit happy, sitting together, surrounded by fireflies.

The film was based on the novel of the same name by Akiyuki Nosaka, who wrote it as a semi-autobiographical short story after surviving the firebombing of the city of Kobe in 1945; he watched his younger sister Keiko die of malnutrition following the bombings, and he wrote the story as an apology to her. The film’s director, Isao Takahata, was compelled to do the story as an animated feature; Nosaka had previously turned down offers for live-action versions, but felt that animated films would better tell the story.

Though Grave of the Fireflies was critically well-received – and is still considered one of the single best war films ever by many critics – it performed poorly at the box office. This had a lot to do with the competition from My Neighbor Totoro, which looked even more light-hearted and fun comparted to the dark and tragic nature of Grave of the Fireflies. However, it’s since picked up a number of awards, and Roger Ebert enjoyed the film so much he once said that it was “so powerful that it forces a rethinking of animation.”