Chiyochan
King
Get out.>>force the player to declare war.
I don't have many ideas, I like the idea of the sea islands because i like colonizing them but if its realistic or not i don't know, what I do know is that Japanese UP is useless, it basically means that if you have to use it you've already lost because of stability; Japan is super densily populated, maybe they could get a special (automatically built) building that increases the size of the cities in their main island and cuts down on maintenance.
Making isolationist powerful is also another idea, as it would give Japan a rather large benefit as the AI who keeps picking the stupid civic, however it still might be weak because eastern nations already have a huge stability bonus on foreign because of the lack of neighbors. The only other idea i could think of is a nice war mongering one, although I hate to play that way; The power of Banzai: Free combat 1 Promotion for all units, Japan never gains negative stability modifiers for losing units in combat.