I actually went to see this without reading the original, worrying about whether or not I should read it first.
But it was interesting. Is it because the original Manga reaches a proper climax?
It would be better to make a drama series like this on Netflix, roughly three seasons long. Even more former inmates could mix with the local population and suddenly appear at the local festival. What happens in the film could be season one, while the project itself still continues, or something like that.