You have very great magic power, even though you look like an ordinary girl.

One day there was a prediction that if you were allowed to live until you were 25 years old, that power would control you completely and it could destroy this world.

The emperor sent a duke to kill you,the duke first approached you first, but over time he fell in love with you, and you are now approaching 25 years old

You actually know that the duke was sent to kill you,but you pretend not to know.