Yoon Joon Sang and Kim Nam Joo express different opinions on their younger siblings' romantic relationship, eventually snowballing into their first real fight.

On July 29's episode of 'Unexpected You', Mal Sook (Oh Yeon Suh) and Se Kwang's (Kang Min Hyuk) mothers find out about their romantic relationship through Mal Sook's drunken confession.

Se Kwang is then forced by his mother to leave his older sister's home until he returns to school in Dae Jeon. Gwi Nam (Yoon Joon Sang), however, tries to stop his mother-in-law. He argues that Se Kwang is an adult and has the right to make his own mistakes and decisions.

Yoon Hee disagrees and tells him that the best thing would be to keep Se Kwang and Mal Sook apart from each other. She also comments, "You don't understand because you haven't lived with your sister Mal Sook for a long time...I've cared for him [Se Kwang] as if he were my own son and that is why I can't let him continue his relationship with Mal Sook."

Gwi Nam is offended at Yoon Hee's insinuation. He replies, "I took your side this entire time because you didn't get along with Mal Sook...Se Kwang is an adult and he needs to take his own responsibility for his actions." Yoon Hee ultimately wins the argument and Se Kwang is forced to leave with his mother. Yoon Hee and Gwi Nam each leave for work without resolving their fight.