壱岐島
During the 1st year of King Taejong's reign in 1401, Yi received his first assignment as a delegate to Japan, where he would travel to Iki Island to repatriate 50 Korean prisoners. Yi continued to commute yearly between the two nations in a diplomatic function to find and negotiate for release Korean captives such that about 500 were freed by 1410. On January 27, 1416, Yi was captured by pirates and was sent to the Ryukyu Islands. He was able to return to Korea, but revisited Ryukyu in the same year to arrange for the freedom of 44 others by July 23.