xxhe
Prince
Played as Korea, there's an easy way to win the scenario.
The key problem is that most of the southern cities and coastal cities will be conquered by Japan in a few turns, and, of course, we can't produce enough units in this short time to defend all our cities. The way I found to cope with it was selling all of them to Nurhaci
When you sell the cities, sign Open Border with Nurhaci. I left Daegu to defend Japan because it's easy to defend. So now Japanese army can only land Korea at a very narrow frontier; while we can use Nurhaci's places to kill Japanese units
Then open the Honor tree, with the help of GG, it's super easy to clean all the Japanese army becasue they all floats on the sea.
At last, when you see Chinese army comes, declare war on Nurhaci, and retake the cities you sold. This is an easy task because most of the cities left undefended.
After you take back 2-3 cities, Nurhaci will come and beg for peace. Since Chinese/Korea allies are much stronger than Nurhaci, Nurhaci will put all his cities on the table for peace. Agreed, and next turn, we win
Attached is a replay information. It's not optimized - I believe that winning within 20 turns should be possible. But anyway, I think this is an exploit or even a BUG that definitely needs hotfix.
The key problem is that most of the southern cities and coastal cities will be conquered by Japan in a few turns, and, of course, we can't produce enough units in this short time to defend all our cities. The way I found to cope with it was selling all of them to Nurhaci

When you sell the cities, sign Open Border with Nurhaci. I left Daegu to defend Japan because it's easy to defend. So now Japanese army can only land Korea at a very narrow frontier; while we can use Nurhaci's places to kill Japanese units

Then open the Honor tree, with the help of GG, it's super easy to clean all the Japanese army becasue they all floats on the sea.
At last, when you see Chinese army comes, declare war on Nurhaci, and retake the cities you sold. This is an easy task because most of the cities left undefended.
After you take back 2-3 cities, Nurhaci will come and beg for peace. Since Chinese/Korea allies are much stronger than Nurhaci, Nurhaci will put all his cities on the table for peace. Agreed, and next turn, we win

Attached is a replay information. It's not optimized - I believe that winning within 20 turns should be possible. But anyway, I think this is an exploit or even a BUG that definitely needs hotfix.