Grave of the Fireflies

From Wikipedia:

Grave of the Fireflies (火垂るの墓, Hotaru no Haka?) is a 1988 animated film written and directed by Isao Takahata.[1] This is the first film produced by Shinchosha, who hired Studio Ghibli to do the animation production work. It is an adaptation of the semi-autobiographical novel of the same name by Akiyuki Nosaka, intended as a personal apology to the author's own sister.

Roger Ebert considers it to be one of the most powerful anti-war movies ever made. Animation historian Ernest Rister compares the film to Steven Spielberg's Schindler's List and says, "it is the most profoundly human animated film I've ever seen."