Sergeant Jeong Cheol-min's squad are in a renovated stock room with no window. The squad members are well known to be a hardworking group until Councellor Hong Yeong-soo comes in and starts causing trouble. Hong Yeong-soo seems to have difficulties adjusting to this environment. Things in the army changes rapidly, Jeong Cheol-min and his crew find themselves under attack perceived as the aggressors.

When a zombie virus pushes Korea into a state of emergency, those trapped on an express train to Busan must fight for their own survival.

Kyungcheon is a pianist-in-training who loses his heart and becomes a milk cow. He lives as a man during the day, but becomes a milk cow at night and eats grass. Meanwhile, with the help of wizard Merlin, a satellite named Ilho fell from the cosmos by a supernova, is transformed into a girl. One day, Kyungcheon is attacked by members of a secret agency that chases people who lost their heart. Kyungcheon defeats them with the help of Ilho. Following a narrow escape from secret agents, the two mismatched characters come to know about each other’s secrets and draw close.

In this animated prequel to "Train to Busan," a group of survivors deals with a zombie pandemic that unleashes itself in downtown Seoul.