I thought that if you played as a damiyo that japan couldn't attack you until you had 10 or more provinces. Well now that you can press claims for vassals japan can attack any of the vassals that have a claim or core on another damiyo. Playing as one of the damiyos I got attacked by japan and all of the vassals within the third month. this happened on 6 different attempts. I would think that it is borderline impossible to beat japan and all of the vassals with only four or so provinces. Anyone have any idea on how to plan japan now or just wait and hope they fix this?