PC: Japanese-Korean Co-empire?

So, is it ASB or could, most likely through personal union, at least that's my bet, Japan and Korea form an empire without one conquering the other?
 
It depends on how far back you want to go. IIRC Pre-Yamato Japan and Korea were quite close. Have this trend continue and you might see a Koreanicized Japan being part of a greater Korea.
 
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