SHIN SEKAI: SPARK OF THE NEW WORLD
this lasted for many years even after the death of Yen until the Nihon army suddenly increased in strength and number and began bombarding Yamato with continuous attacks.
Their walls were gone, their army depleted, thousands dead, and no hope of survival until one man came up with a very crazy idea that worked. His name was Shin Mikazuchi, son of Yen Mikazuchi and his idea was a mass exodus. while all the people of Yamato left the island he would stay behind and hold off the enemy. the people of Yamato immediately prepared and took off before Nihon could launch attack.
It is believed that Shin ran through the walls of Nihon and massacred every living person. some say he knew that the island