Gu Sera

Gu Sera, the number one troublemaker at Gangsan High, the most notorious high school in the entire country. As a child, she secretly harbored a crush on her boarding house oppa, Lee Seojoon. Now, he arrives at Gangsan High for his teaching internship, only to face endless challenges with its unruly students. Determined to protect her crush, Gu Sera decides to transform the nation's most problematic high school into a model institution!

(Source: Naver, translated)