Haejin's First Love

The characteristics of "First Love" Disease are:
1. The majority of the patients are in their teens,
2. Those patients are in love with someone,
3. There formed a heart-shaped scar on the patient's body.

Haejin Jeong never caught the disease, even though all of her friends had. But when she hit 24 years old, two men miraculously appeared in her life as if it were fate. The question is, which one is her first love?