The franchise of Ichi the Killer is much bigger than you would think. For the 2000s standards, Ichi the Killer was one of the few works that got made as a live action movie, as an animation and had a Manga at the same time.
These are keywords when it comes to Ichi the Killer: engagement and immersion. I cannot stress that enough and there is a reason why.
In terms of adaptation and as a standalone movie, Sakuran is one of the best I have seen.