Japanese Intelligence Agent
"Kato Kiyomasa will cross the sea on this date; ambush him now."— False intelligence supplied to Joseon military officers.
Yoshira (要時羅) was a Japanese intelligence operative under Tsushima Daimyo So Yoshitoshi who played a pivotal role in the Japanese counter-intelligence plot that led to Admiral Yi Sun-sin's dismissal prior to the 1597 invasion.
Fluent in Korean and well-versed in Joseon customs, Yoshira was sent by his master So Yoshitoshi to establish contact with Joseon military commander Gim Eung-seo. By providing accurate minor intelligence regarding Japanese troop movements over several months, Yoshira earned the trust of Gim Eung-seo and the Joseon royal court.
In early 1597, as Hideyoshi prepared for a second invasion (Jeongyu Jaeran), Yoshira delivered crucial counter-intelligence: he claimed that Japanese general Kato Kiyomasa would cross the sea on a specific date, advising Joseon's navy to set a trap. King Seonjo ordered Admiral Yi Sun-sin to sail out immediately. However, Yi Sun-sin suspected an enemy ambush in treacherous sea terrain and hesitated. Seizing upon Yi's caution, Japanese agents spread rumors of disloyalty.
Tricked by Yoshira's double-agent scheme, the Joseon court arrested Yi Sun-sin for disobeying royal orders and replaced him with Won Gyun. Shortly thereafter, the unprepared Joseon fleet under Won Gyun suffered total destruction at the Battle of Chilcheollyang. Yoshira's espionage is remembered as one of the most devastatingly successful counter-intelligence operations of the Imjin War.