Song Hyeonji and Jang Chanwoo have always been friends. Since childhood, they'd shared everything: toys, food, memories, etc. But when Hyeonji realizes her true feelings towards the boy she'd always thought of as a brother, what will she do? Enter Lee Kwangmin: notorious for being rude and unkind to those he doesn't know, he surprisingly decides to help Hyeonji win over her crush. But will it go right, or will the mission to make Chanwoo like her go in a completely different direction?