Nice Sister-In-Law 4: Brother-in-law, I will fill your vacancy now! His younger brother Min-hyeon lives with his older brother Jun-hyeon. Pyeong-seok, who was burdened by living in the same house with his brother-in-law, keeps his eyes on Mi-jeong, the young and sexy wife of his older brother. He even imagines sharing love with his brother-in-law at the sound of a strange moan from the next room. One Sunday, my older brother is away from home in a hurry for work, and the two of them are left alone with a strange feeling...