For the crime of negligence and for abandonment of his men impending enemy attack, Yi Soon-shin is stripped of his rank and ordered to serve the military as a common soldier. The newly appointed garrison captain of Chosan Fort Yi Unryong is baffled by the soldiers who look upon the defeated captain Yi Soon-shin with admiration and respect. After being attacked by Ulginae and realizing the enemy's strength, Yi Unryong turns to Soon-shin for help.
—https://www.yidio.com/show/the-immortal-yi-soon-shin