I have had some more time to think about the news of Tanaka Koki's firing from Johnny's & Associates so I have decided to share them. As someone not really following KAT-TUN closely I know I could be missing something but here are my thoughts about it anyway.
So from J&A's announcement Koki had been let go of back on September 30th, which means the latest scandal photos probably were not the cause, more like J&A wasn't going to cover for someone who was no longer in their agency so they did nothing to stop them from going to print. Otherwise they probably would have paid whatever price the magazine would have asked for those as they are much more damaging than the usual dating/sex rumors that get printed.
At worst they knew about the photos before his contract was terminated and let it be the straw that broke the camel's back, but this is probably going to be information that we will never know unless Koki decides to spill about it, which could get him black listed by Johnny's no matter what he decides to do in the entertainment industry.
I think then what must have gotten him in trouble with them had to have been the night club he invested in, DJ-ing at clubs without letting them know and not enforcing the "no photos" rule when he ran into fans. Perhaps there could have been more but I think those are the rumors that had the most proof behind them. There are rumors about him using drugs which if they were true could be the main reason that he was dumped as Japan in general has a zero tolerance stance with drug use and he would be far from the first Johnny's dropped from the agency because of discovered drug use.
It also seems like this was something that was an issue for a while and only recently came to a head and ended with his termination from the agency. There is no other way to explain why the members of the group would have had a final group meeting about the issue if it was not a known issue. Also back on October 5th his brother, Juri, wrote a comment on the Juniors' R no Housoku Blog that sounded like he was weighing in on the issue by saying that he would keep admiring someone even if others would question it. Only the fans were left in the dark about it until now.
It's so sad things ended the way they did, as I cannot really see KAT-TUN without him as his raps helped make their songs stand out. And I just cannot picture the group with only four members. At least with NEWS the remaining four had done things as four so fans could see how things would continue on with them. With KAT-TUN there seems to be so much uncertain, and it does not help that Kame will be releasing a special project CD without the group. But I would not be surprised if we get something from the four member KAT-TUN eventually. But until then it will probably be hard to dismiss the fears of the fans of the group.