Why does the Akira film end differently from the manga?

Spoiler note: this page compares both endings directly, so it gives away how each one closes.

The dates are the whole answer in outline. Katsuhiro Otomo's manga ran in Kodansha's Young Magazine from December 20, 1982 to June 25, 1990: 120 chapters and more than 2,000 pages, later collected in six volumes. The film, directed by Otomo himself, opened in Japan on July 16, 1988, and its main production was already complete in 1987. A two hour film had to be built, and closed, out of roughly the first half of a story whose second half did not exist yet.

Otomo's own account of the method is specific. The film project, he recalled, had to begin with the writing of an ending that would bring suitable closure to the major characters, storylines and themes without being extraordinarily lengthy, so that he could then work in reverse order and decide which elements of the manga would make the cut into a lean, two hour story. He later called making the film before finishing the manga "the worst possible idea". He came to like having two similar but different versions of the same story, while still feeling that too much of the original had been cut out of the film.

What that forced choice looks like on the page and on the screen is starkest at the figure of Akira himself. In the film, Akira is already dead: Tetsuo digs beneath the Olympic Stadium and finds only remains sealed in jars for scientific research, and at the climax the espers revive Akira to draw Tetsuo into another dimension in a singularity that mirrors the destruction of old Tokyo. In the manga, Tetsuo frees a living boy. Akira wakes, and when the esper Takashi is killed in the struggle over him, Akira's grief triggers a second destruction of Neo-Tokyo in the middle of the story, not at its end. The manga then continues for three more volumes the film never touches: the ruined city divided between Lady Miyako's temple and the Great Tokyo Empire, an international military intervention, and a finale in which Akira cancels out Tetsuo's final explosion with one of his own before Kaneda declares the city's sovereignty and rides through a Neo-Tokyo that is beginning to restore itself.

The film also sits inside the manga's own calendar. Otomo paused the serial between chapter 87, on April 20, 1987, and chapter 88, on November 21, 1988, a break of about nineteen months that brackets the film's production and release. When he finally closed the manga in 1990, he has said the inspiration for its conclusion arose from a conversation he had with the filmmaker Alejandro Jodorowsky. Two works, one author, two endings: the first written because a film cannot wait, the second written two years later because the story was still his to finish.