About the ending.

I have another interpretation.

To me the ending showed the line between American culture and Japanese culture, in terms of brotherhood and the likes, how each sees and practices it. At the end we saw Epps' character, Denny, kept on complaining and wondering about his situation, unappreciating for minutes long even after Kitano'd just helped him run away. I mean I got why he acted like that, he had every reason to, but in this context that was kinda too petty of him, considering the how close them two were. Noticeably, his reactions then somehow showed that he only cared about himself and not about Kitano's character, Aniki, or his fate, or what he would do later on with the mafia. It dragged and unnecessary. This kind of thing took me back to a scene earlier, when Shirase asked him why he didn't follow Aniki home and he just answered plainly that Aniki didn't want anyone to know his whereabouts so he just ignored it. And what do you know, when he saw the money in the bag, he started changing his mood and attitude, thanking the guy and stuffs. "Brother", singular afterall. It's a one-sided relationship, Aniki cared much for those whom he considered brothers, and Kato reponsed back the same while Denny didn't really.

To think about it, when interpretating the ending this way you don't necessarily have to take it as a bash against American culture or stuffs like that, to me the basic point this film was trying to deliver was of how the term Brother is taken in Japanese culture, specifically, in yakuza Japanese culture. It's different, and not many people outside the yakuza system get it right. His half-brother went to the States and got influenced by American culture, thus he was just like Denny, only cared for his own life.

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