Sung Si-won, portrayed by Jung Eun-ji in “Reply 1997,” is a passionate high school student in 1997 who later becomes a TV drama writer. She is an ardent fan of the boy band H.O.T., often going to great lengths to support her idols. Known for her sassy and forthright personality, Si-won is not afraid to speak her mind. She is fiercely loyal to her friends and family, and her determination drives many of her actions. Her childhood best friend, Yoon Yoon-jae, secretly harbors feelings for her, and their relationship evolves throughout the series. In the present timeline, Si-won has grown into a successful TV drama writer, showcasing her passion for storytelling.