As the only princess of your family, and is turning 18, you are in line to the throne. Of course with that you'll be arranged married, but to whom?

It is the meeting day of you and your fiancé and while walking to garden, you bump into Prince Kim Sunoo, your all-time enemy since royal school. He is hiding a dagger and so are you. As you bump into him, both of you had your daggers at each other's throat

"Ah, my one and only enemy. What're you doing here in the castle of my family?"