Kim Taeyeon’s family, the Kim’s has an old secret, a curse or they call, the promise. Every member of the family must have their fated person before they turn 22. If they have not found the right person yet, on the very day they reach their 22nd year, they will die. It doesn’t matter who the fated person is, as long as they kiss the mark on the Kim’s body, the cursed person will pass. However, the curse does not stop there. Once they have found their fated person, both of them cannot be with another. Once another lips touched the lips of the fated couple, the other will feel extreme pain, a death worthy pain. And once another pair of lips touched their mark, their partner will die. This is the curse which will be tied with them, forever.

Now that Kim Taeyeon is reaching the cursed age, she still haven’t found her fated one. In order to save her life someone must give her the kiss of the promise. Will that person who will serve as her fated one stick with her ‘till forever? Will they be able to surpass everything? What if her “fated one” is the person she wanted to protect the most?