I think the author chose the title because the word impyrium is very close to the word imperium, which means absolute power. The story is about a girl named Hazel that is in line to the throne with ancestors of magical powers. Her grandmother says to become more powerful or her tutor will die. At the end of the book, Hazel learns that her grandmother wanted Hazel to bring terror to the other ruling families, by losing control of her powers, as it says on page 582, “‘ My grandmother wanted me to turn into a weapon, to make people fear our family again.'”. I think that her grandmother wanted more power although she was the most respected person as the divine empress. If I could choose the title, I think I would have chosen The First Faeregine because her grandmother says on page 102, “‘She’s not the last Faeregine, you fool. She’s the first in a thousand years!'” So I think that Impyrium is a good title as well as Empire.