The film begins at Sannomiya Station on 21 September 1945, shortly after the end of World War II. A boy, Seita (清太?), is shown dying of starvation. Later that night, having removed Seita’s body, a janitor digs through his possessions and finds a candy tin which he throws away into a nearby field. The spirit of Seita’s younger sister, Setsuko (節子?), springs from the tin and is joined by Seita’s spirit as well as a cloud of fireflies. Seita’s spirit then begins to narrate their story accompanied by an extended flashback of the final months of World War II. The flashback begins in Kobe on 16–17 March 1945, with a fleet of several hundred American B-29 Superfortress bombers flying overhead. Setsuko and Seita, the two siblings, are left to secure the house and their belongings, allowing their mother, who suffers from a heart condition, to reach a bomb shelter. They are caught off-guard as the bombers begin to drop thousands of incendiary bomblets, which start huge fires that quickly destroy their neighborhood and most of the city. Although they survive unscathed, their mother is horribly burned and dies a short time later. Having nowhere else to go, Setsuko and Seita move in with a distant aunt, who allows them to stay but convinces Seita to sell his mother’s kimonos for rice. While living with their relatives, Seita goes out to retrieve supplies he had buried before the bombing. He gives them all to his aunt but hides a small tin of Sakuma fruit drops, which becomes a recurrent icon throughout the film. Their aunt continues to shelter them, but as food rations continue to shrink, she becomes increasingly resentful and openly remarks on how they do nothing to earn the food she cooks. Seita and Setsuko finally decide to leave and move into an abandoned bomb shelter. They release fireflies into the shelter for light. The next day, Setsuko is horrified to find that the insects have all died. She buries them all in a grave, asking why they had to die, and why her mother had to die. What began as a new lease on life grows grim as they run out of rice, forcing Seita to steal from local farmers and loot homes during air raids. When he is caught, he realizes his desperation and takes an increasingly ill Setsuko to a doctor, who informs him that Setsuko is suffering from malnutrition but offers no help. In a panic, Seita withdraws all the money remaining in their mother’s bank account, but as he leaves the bank, he becomes distraught when he learns from a nearby crowd that Japan has surrendered unconditionally to the Allied Powers. He also learns that his father, a captain in the Imperial Japanese Navy, is probably dead since nearly all of Japan’s navy is now at the bottom of the ocean. He returns to the shelter with a large quantity of food, only to find a dying Setsuko hallucinating. Seita hurries to cook, but she dies soon after. Seita cremates Setsuko’s body, and puts her ashes in the fruit tin, which he carries along with his father’s photograph, until his death from malnutrition in Sannomiya Station a few weeks later. In the film’s final scene, the spirits of Seita and Setsuko are seen healthy, well-dressed and happy as they sit together, surrounded by fireflies. The camera then moves overhead, showing the two of them looking down on the modern city of Kobe.
14岁的初中生清太与6岁的妹妹节子原本生活在军官家庭，父亲是日本联合舰队的舰长（当时的军官家属待遇是非常好的），父亲出去打仗了（和美国人），留下妻子和两个孩子。美国人的轰炸机来 袭击时，母亲被炸身亡，兄妹俩去了亲戚阿姨家。由于战时物资紧张，阿姨家本来就有4个孩子（老公也被充军去打仗了，不久战死。真人版中还加了个瘸腿的小 叔），这下清太和节子来了后原本就吃不饱的一家就更显得捉襟见肘。在阿姨的冷言冷语下，兄妹俩终于决定出走，独自生活。在一个废弃的小山洞中，他们建立了 自己的天地，没有大人帮助他们， 清太为了照顾年幼的妹妹，想方设法去搞吃的东西（偷东西）。虽然要自行找寻食物维生，但生活刻苦之余，他们也像其他小孩一样活泼好动，闲来在杂乱下的田间 玩乐，夜晚更一起在草地上观看漫天飞舞的萤火虫。可是快乐的日子不长，妹妹的身体日渐消弱，最后妹妹因身体衰弱而死。清太始终坚信身为舰长的父亲会为他们报仇，等父亲回来苦日子就到头了。但在后来得知联合舰队已经全军覆没后，唯一的亲人——节子也因长期营养不良而死去，清太也没有了活下去的动力，最终饿死在街头。 《萤火虫之墓》是宫崎骏风格中，被誉为最感人最温馨的一部，兄妹情与战乱的描写入木三分，赚人热泪。《再见萤火虫》，这篇动画是忠实地改编自著名的同名小说。宫崎峻用最富童趣的艺术表现形式揭示了战争的残酷，成就了这部动画经典。 《萤火虫之墓》作为高畑勋进入吉卜力的第一部作品，也是他将自己现实主义题材的创作提高到新的高度的里程碑。该片中他进一步追求现实主义和客观性，采用双重结构的方式构思，在结尾部分展现了今天的神户，以强调现代与过去的对比。 对此，高田自己曾说：“我并不是仅仅讲战争的悲惨，而是希望观众能联想到现代社会人与人的关系，找出现代社会中孩子们异化的症结所在。” 高畑勋写的《萤火虫之墓》剧场大纲摘录 如 今，家庭成员之间的联系以及邻里之间的团结变得越来越弱了。取而代之的是，我们被社会约束下的不同阶层保护着。我们把相互间的不干扰作为相互关系的底线。 并出于好玩的但无关紧要的考虑对他人表示亲切。并不需要一场战争，只要有一场天灾发生并摧毁社会的约束，失去人们之间的相互帮助及合作的想法，那么人们在 与他人的自然关系中将不可避免的显露其贪婪的本性。这使我认为我可以站在任意一边。即使一方尝试逃离人类圈去和他的妹妹单独住在一起，有多少男孩，或是人类，可以可以持续的守护自己的妹妹和清太一样长久？