Keep Circulating the Tapes: The original, fully uncensored version of the movie has never been released to the public and it’s speculated that Toei lost the original negatives. However, the Italian VHS of the movie does feature quite a few of the original uncensored scenes.
Missing Trailer Scene: The teaser trailer made to promote the movie basically has zero animation that was used in the movie (and is noticably more on par with the TV anime in terms of quality). In particular, one shot shows a purple-skinned character◊ who does not appear at all in the final movie. Some speculate that he's supposed to be a mutant born of the radiation caused by the war, but it's never been confirmed.
Role Reprise: Aside from a couple exceptions, every voice actor involved with the anime that was airing at the time reprised their roles, including Akira Kamiya as Ken, Kaneto Shiozawa as Rei and Kenji Utsumi as Raoh.
As shown in the first theatrical trailer, Heart was going to be renamed “Elephant” to keep with the theming of Jagi’s minions (i.e., Jackal and Fox), but in the end he kept his original name.
The first teaser trailer, while probably just a proof of concept since it has animation more in line with the TV show, does feature some oddities compared to the final movie, including a shot suggesting that Rei was going to fight Boss Fang and Raoh sporting a completely different color scheme.
The second teaser trailer, while this time more in line with the movie’s artstyle, features screenshots from scenes not seen in the movie at all, suggesting that they either cut or never animated at all, including:
A shot of Rei landing a hit on Ken, suggesting that they were supposed to have an actual fight compared to the one they had in the final movie.
A shot of Airi, Lin and Bat running through a subway. Also, Lin still has her TV anime design.
A shot of Ken holding Yuria, who seems to be unconscious. This one was actually used quite a lot in promotional material.
A shot of Uighur seemingly hunting Bat and Lin down at an unspecified village.
Reportedly, the original cut of the movie didn't feature a title card reading "END" and they were seemingly considering doing a sequel, but they changed their minds at the last minute, probably because it would've been difficult to adapt the later chapters of the manga with the changes and omissions they did for the movie.
Facts
John Cena has said that this is his favorite animated movie ever.
◊ who does not appear at all in the final movie. Some speculate that he's supposed to be a mutant born of the radiation caused by the war, but it's never been confirmed.
