Junjin a bachelor, one of the member of Shinhwa, fell in love with a girl who is 9 years younger than him, a girl at first he sees and treats only as his little sister, Hyoyeon. They knew each other since he was on his group debut era and she was still a trainee. But that little girl grown beautifully and after being partnered with her on a variety shows, his feeling towards her changed. What will be their fate? Will he be able to be with her?

This is my regret, for not able to realize my true feelings sooner. My regret for being stubborn to admit my feelings. And after all this time, I finally realized that I've lost her.

Hyoyeon hated her husband, Donghae since their marriage was arranged. She hated him so much and become a spoiled wife for him, but he truly loves her. Until one day, Donghae had an accident. When she was arranging his stuffs, she found his diary. At that moment, she regreted all her behaviors to him.