Park Mina is in love with her best friend Yeo Changgu but he has a girlfriend. Mina finds out Lee Jihee (Changgu's girlfriend) is cheating on him and informs Changgu but he doesn't believe her. He believes Jihee who he's known for a total of 9 months over his best friend who he's known since childhood. This causes a fight and for them to end their long term friendship and for Mina to kind of rebel.