With unification of entire Japan in front of him, Toyotomi Hideyoshi sends another envoy to Chosun demanding Sonjo to come before him, but Sonjo pays no attention. Consequently, Japanese envoys So Yoshitoshi and Genzo go to Prince Kwang-hae and Sung-ryong and show them a musket. Witnessing the great power of handheld guns, Kwang-hae asks Sung-ryong to make a request for an envoy to be sent to Japan. While Japan is preparing an invasion, the royal court of Chosun is caught in a political dog fight centered around Chung Yuh-rip's attempted overthrow, and even the military officers including Yi Il are running around hustling to save their own head between the two factions. While the Purge of 1589 is in progress, Soon-shin is put in charge of the King's safety as a Royal Bodyguard and Messenger.
—https://www.yidio.com/show/the-immortal-yi-soon-shin