In an anime forum, I posted the titular question, which was responded by this answer below :
This in turn got me more interested about Korean history. Say, how do you think Korean hegemony or at least partial occupation over Japan will perform here, and for how long will it last ? I'm quite excited by the motions of Korean community established in Japan (which will most likely remain distinct from the natives if they're based on Kyushu) and a more open Japan in general (even with only Kyushu, I don't think its later reconquest by Japan will eradicate the trade connections with Asia established there by the Koreans. If anything, they'll just overtake it).
On the other side of the fence, there are some interesting notes. First, Zen Buddhism received a boost from victory over Mongol-Korean invasion, so did Japanese exclusivist tendency. Second, the opinions between Shogunate and the Imperial court differed about Mongol vassalage. The later was willing to submit but due to their political impotence nobody listened and the Shogunate persisted to refuse Mongol demands. The interesting part about it is that around this time The Imperial Court was still vying to wrestle effective political power from the Kamakura Shogunate(indeed, years after the Mongol invasion, Emperor Go Daigo plotted to overthrow the Shogunate). Had Kyushu fallen, I wonder if the Imperial Court's opinion will catch enough ears, which in turn raise the question how will Mongol-Goryeo campaign for Japan conclude afterward. Here are several possibilities that I can think of :
1) Japan decides to surrender after the fall of Kyushu.
2) Japanese civil war between Kamakura and Imperial Court will follow the fall of Kyushu, which will certainly be exploited by the invading force.
3) Japan remains united in resistance to Mongol-Goryeo advance.
I wonder which of the three possible scenarios would be the most likely to happen, and how it will conclude. Thoughts ?
The Mongol-Goryeo forces were pretty close to taking all of Kyushu in the first invasion, but it failed when the Mongol commanders chickened out and ordered the retreat to the boats, eventually being sunk. The second invasion, on the other hand, had almost no chance of succeeding, with the Japanese being ready.
If the Mongols hadn't boarded their ships during the typhoon of the first invasion, they could have taken Kyushu in that attempt. There seemed to have been a clash between the Koreans (who advocated staying on land) and the Mongols (going back onto the ships), and OTL was decided by the Mongols. With the Japanese forces having their back to the wall (only one fortress remained), an intact invasion force would have been able to conquer Kyushu and perhaps head for Western Honshu.
The one change which would be needed to have the first invasion be successful (not necessarily conquering Japan, but succeeding in invading Japan): Don't get on the ships. Really, the thing was that Kyushu was about to fall, with reinforcement being weeks away. One more push by the Mongol-Goryeo forces would have meant complete occupation of Kyushu.
Should the invasion had succeeded, I can see Korean influence being dominating in Japan. The unique position of Goryeo within the Yuan sphere had allowed the Goryeo king to have the title "King of Shenyang," a basis that would later result in Yi Songgye's rebellion when he was sent to invade Liaodong. Given that the most important fighters of the Mongol forces were the Koreans, and it was the Goryeo King at the time (Chungnyeol) who ultimately pushed for the invasion of Japan, I can certainly see the Goryeo court having great influence over the affairs of the conquered Japanese islands.
The question is, how would the Goryeo court have influence in the conquered parts of Japan. I can see three ways to this:
1. Trade/Cultural exchange: With the subjection of Japan, the threats from the Wakou pirates would have decreased, and as such trade and cultural exchange would most likely have been higher. Korea would most likely have recovered far faster from the damages of the Mongolian invasions, and the higher population would only have to face the dangers mostly from the north. Also, influence would naturally grow.
2. Population movement: The "King of Shenyang" title was originally given because of the large amounts of Koreans who moved to and lived in Liaodong. If Japan is occupied, I can see a sizable number of Koreans going to Kyushu, and setting up communities. This means that Koreans would be setting root in Japan as never before since the fall of Baekje, and that in itself would be another strength for Goryeo.
3. Title: It was the Goryeo King that pushed for the invasion, and as such he would have a say in the administration of Japan. Even a small role would have large repercussions, and there is always the possibility that he would have received an honorable title concerning Japan. This would most likely link Korea to Japan. Add in possible intermarriages between the royal families of Yuan, Goryeo, and Japan, and you have in-laws connecting from Dadu to Kyoto.
This in turn got me more interested about Korean history. Say, how do you think Korean hegemony or at least partial occupation over Japan will perform here, and for how long will it last ? I'm quite excited by the motions of Korean community established in Japan (which will most likely remain distinct from the natives if they're based on Kyushu) and a more open Japan in general (even with only Kyushu, I don't think its later reconquest by Japan will eradicate the trade connections with Asia established there by the Koreans. If anything, they'll just overtake it).
On the other side of the fence, there are some interesting notes. First, Zen Buddhism received a boost from victory over Mongol-Korean invasion, so did Japanese exclusivist tendency. Second, the opinions between Shogunate and the Imperial court differed about Mongol vassalage. The later was willing to submit but due to their political impotence nobody listened and the Shogunate persisted to refuse Mongol demands. The interesting part about it is that around this time The Imperial Court was still vying to wrestle effective political power from the Kamakura Shogunate(indeed, years after the Mongol invasion, Emperor Go Daigo plotted to overthrow the Shogunate). Had Kyushu fallen, I wonder if the Imperial Court's opinion will catch enough ears, which in turn raise the question how will Mongol-Goryeo campaign for Japan conclude afterward. Here are several possibilities that I can think of :
1) Japan decides to surrender after the fall of Kyushu.
2) Japanese civil war between Kamakura and Imperial Court will follow the fall of Kyushu, which will certainly be exploited by the invading force.
3) Japan remains united in resistance to Mongol-Goryeo advance.
I wonder which of the three possible scenarios would be the most likely to happen, and how it will conclude. Thoughts ?