Your name is Park Yuna. You met this girl, Lee Soon Kyu. She would rather be called Sunny. You became best friends and promised to keep it that way, forever and ever. Then both of you moved to a new school, where you met Choi Soo Young. You sat beside each other. Not long after that, you began to know her better. You liked being friends with her. Did you break your promise with Sunny? What will happen to her? Will she be replaced?