Assuming a POD where Japan became an Orthodox country, how will this change the political dynamics of East Asia?
Maybe you could have Catholicism become really big in Japan, before the Emperor/Shogun pulls a Henry VIII and has himself declared head of the Church in Japan. If he doesn't change any other doctrines, you'd have a Japan which is essentially an Orthodox country. If so, you'd probably have no Sakoku policy, although I don't feel qualified to say what effect that would have.
Kind of odd to call it an Orthodox country, since it's arguably applicable only to those of the Byzantine Rite (or non-Chalcedonian rites in the case of Oriental Orthodoxy). Protestant seems like a closer description, despite clear contrasts in doctrines and all.
Would rather see a Buddhist/Hindu/Zorastrian Europe thread than another of the plethora of "what if Christians took over everything" wank.