The Suspects of Necromancy

Do you want eternal life? Red eyes, white skin, golden hair... Luna, our protagonist, is an apprentice magician who was bought by Khan, a shabby old magician. Luna is a prideful girl who spends her days learning magic in order to impress Khan, who has no interest in anything other than the study of magic. Then, the previous king dies of illness, and rebellions erupt in various parts of the country. The kingdom is on the brink of destruction, but an army of undead attacks the rebels and puts them down. Who in the world has used the forbidden necromancy?