With lawyers so rare in Japan, the net is as good place to start as any. The problem is finding the information on-line and in English...
Common sense would say though that if your name is not on the title or lease, and if your wife divorces you and removes your name from the family register, you have few legs to stand on. The police tend not to get involved in family disputes, though that is changing. But once you are out of the family, if your ex-family raises a big enough stink, they can probably get you booted out right quick.
Sorry things are going so poorly.