What would you do if you were the person that wasn't the main character in the story?  What if you were just a minor character watching from afar as the person you were in love with loved another?  

Seunghyun is Yoona's best friend and even though he has doubts about her boyfriend, he puts it aside because for one, she doesn't listen that her boyfriend isn't good for her, and she's completely blind from love.

Jessica is Jiyong's best friend, and she's been in love with him ever since, but after seeing how happy his girlfriend made him, she puts her feelings aside for Jiyong's good.  

BUT what will Seunghyun and Jessica do once they see that their best friends are being fooled?