The Villainess Once Said

"On this day, six years from now you will die. Della Limiere, because you are the villainess of this novel." Envious of the opportunities she never had as a girl and eager to learn about new things, Della hears a shocking prophecy from Lissha. She must change her fate and marry a supporting character in order to survive. But why is the emperor threatening this guy and why was he almost assassinated? Is he really just a supporting character? Then fate takes a turn, and the truth becomes a lie Will Della survive to the end?