Min-wook loves his roommate friend Yeongsu's older sister, Sujin. However, Sujin will soon marry a man who meets the condition. I try to hide my heart and wish my sister happiness, When she sees her divorced a few months later, the old feelings come back to life. Soo-jin, who is divorced, will stay in her sister's house for the time being. Min-wook and Su-jin, who have been in one house, are now trying to confirm their love for each other...

In 'My Friend's Older Sister', a man finds himself falling for his friend's older sister, leading to a passionate and forbidden romance. The story explores the complexities and consequences of their relationship.

When I was a high school student, my sister was a sexy friend who kept me from falling asleep with all kinds of delusions every night. Min-soo's thrilling delusion catches fire after she accidentally meets her naked sister at home. After becoming an adult, Minsu and his friend Yong Joon get a job at a sister company. From her sexy friend, Minsu's secret work towards her, who is now reunited as a sexy female warrior, begins...

Minsu quits the company if he takes it because he is far from home. So, as a special measure, I will stay at my friend's house for a while. Min-soo falls in love with Jae-seok's older sister Yoon-jung at first sight. Meanwhile, Jae-seok decides to start living with her girlfriend Hae-ju at home. Min-soo and Yoon-jung are alone, and love grows...