Background --
The First Emperor of China was growing old. His sanity was questionable (due to suspected mercury poisoning). His eldest son was an idiot - and would not live past the Emperor's death. His youngest son was a spoiled brat. Building the Great Wall could be seen as an act of desperation - conquering the world is a young man's job and his sons were not up to the job... unless Xu Fu is successful...
But then Xu Fu was sent off into the horizon never seen again - with the hopes of bringing his emperor immortality. Many historians suggest he might have reached Taiwan, various parts Korea, Japan, Ryukyu, and one even suggested the Americas.
Now for the basis...
Xu Fu lands in Japan - can he conquer it?