My Sister’s Duty

Synopsis

Dongwoo, who happened to found the secret of his squad leader is spending a hellish day because of it. Jungyeon, the younger sister found out about her brother’s suffering through his diary. To protect her brother whom she loves more than anyone else, Jungyeon visits Yoo Jinho, the squad leader… “Oppa… I’ll protect you this time.”

Also known as My Younger Sister's Duty / Sister Duty / Dongsaengui Uimu / 동생의 의무