Seo Kang Jun's post-military transformation has caught the attention of many, especially as he shows a notable difference from his chubbier pre-enlistment appearance.

This change has generated even more excitement for his upcoming role in the MBC drama 'Undercover High School,' which is scheduled to premiere on February 21 at 9:50 PM.

The first teaser poster for the drama, released on January 16, showcases Seo Kang Joon as Jeong Hae Seong, an elite agent of the National Intelligence Service (NIS). 

In the poster, Seo Kang Joon is seen wearing a school uniform, standing in a dimly lit corridor with a determined look on his face. With a gun in hand, he exudes an air of intense charisma, heightening the tension. The shadowed side of his face subtly reveals the duality of his character as a student undercover as a NIS agent.

In the drama, Seo Kang Joon’s character, Jeong Hae Seong, is assigned a special mission that requires him to infiltrate a high school while posing as a student. Throughout his school life, he will not only complete his secret assignments but also interact with his peers in unexpected ways, promising an intriguing and unpredictable plot.

The production team explains that the teaser poster’s use of the contrasting elements of a school uniform and a gun effectively conveys the concept of an NIS agent posing as a student. The image of Jeong Hae Seong standing resolutely in front of the classroom signals the start of the 'Undercover High School' mission.

'Undercover High School' follows the story of a National Intelligence Service agent, disguised as a high school student, who embarks on a chaotic journey to find missing royal gold bars. The drama is set to offer a combination of thrilling action and humorous high school moments.

'Undercover High School' will debut on MBC on February 21 at 9:50 PM.

SEE ALSO: 'Undercover High School' unveils new still cuts of Seo Kang Jun and Jin Ki Joo before premiere