So I just united Japan as the Emperor. As in the OPM that has no diplomatic options with anyone.
(this province was the last stronghold of the Shoguns)
I was half-expecting the Shogunate to not dissolve, which would've put me in a quite interesting spot, utterly unable to conduct war.
Thank god for the "Trading in Spices" bonus, would've been so much harder without. Also would've been impossible had Korea not randomly decided to invade and then white peace out; that distracted Minamoto long enough for me to collapse their country.