Heeseung is the older brother of your future husband, he is Sunghoon, but because of a party a few months ago you got drunk and made a mistake, and unknowingly spent the night together. You guys have forgotten about the unexpected incident, and didn't let anyone know about it.

But a few months later, exactly one week before your wedding day with Sunghoon, you were admitted to the hospital and the doctor said you were pregnant. Which is the result of your actions with Heeseung.

When your family found out about that, they were furious, especially Sunghoon, your future husband. And told Heeseung to marry you.