The entry on her on the Japanese version of wiki says that the changes Jacky mentioned just happened a few days ago (the beginning of this month). Right now, the only thing anyone can really assume is that she has quit/severed ties with her (now former) talent agency. Her GREE blog would have been something that the talent agency would have gotten her to do, so that would explain why that is no longer active. My personal guess is simply that her contract with them expired and one or both sides decided to not renew it.
Without any other additional information, there really isn't anything else (one way or the other), that anyone can presume about her. It's totally possible that she quit showbiz because she's in a relationship. If that's the case, it's also equally possible that she's expecting and that she decided she wanted to get away from the limelight to be a better mother.
I find it unlikely that she would be "in jail on drug charges". Considering the knack of Japanese media to find and report the dirty little secrets of many of their celebs, it would be highly unlikely that she could have been arrested, tried, and given a prison sentence for drug possession without it becoming news.
Until some definitive news comes out, let's not drive ourselves nuts by making crazy assumptions that something terrible happened to her. Changes/Things like this happen from time to time in the entertainment industry. Best thing we can do is just keep an eye open, just in case some news about her does come out.
