Cheon Seo-Jin, portrayed by Kim So-Yeon in “The Penthouse: War in Life,” is one of the primary antagonists of the series. She is a wealthy and glamorous soprano singer who becomes the Head of the Arts Department at Cheong-A High School. Seo-Jin is characterized by her extravagant arrogance and ruthless ambition. She will go to any lengths to achieve power, money, and pride, often engaging in manipulative and criminal activities. Seo-Jin’s character arc is marked by intense rivalries, particularly with Oh Yoon-Hee, and her tumultuous personal relationships, making her one of the most memorable and dynamic characters in the series.