The Saint's Magic Power is Omnipotent (Manga) Vol. 9

Having returned to the royal capital from the Klausner Domain, Sei resumes her busy schedule subjugating monsters, and it isn't long before all the black swamps in the country have been purified and the number of monsters has declined. Sei is looking forward to a breather, but then it's announced that her formal debut as the Saint will be at the start of the social season--on the same day as the ball hosted by the royal family!