Wonwoo is your childhood best friend. Both of you are close, to the point where your parents know each other and your families are also really close. He's the only child, while you? You have a four-year-old little sister; you're the oldest.

One day, your mom left your sister at your place. Wonwoo is also at your place at that time. He played with your little sister while you were in your room, and you just finished showering. Your parents often tell you that your sister likes Wonwoo more than you.