First, she needed to get someone to pretend to be the Black Witch. She chose Emma because she would always be reading in the library. Second, she needed to get Al to wander the world and kill as many people as possible to feed the ring. Her method to return home required a lot of sacrifices. Al was chosen because he was close to Emma. Third, make sure the Black Witch does not disturb this plan until enough sacrifices were made. The ring hid Al's presence. Fourth, die as a saint. In reality, Luna was watching everything from a far.

It took the Black Witch eight hundred years to find Al and dispell the ring. Is what the Black Witch thought. The truth was Luna dispelled the spell as she has enough sacrifices to go back home.