The Ancient Magus' Bride: Those Awaiting a Star

A prequel to the manga The Ancient Magus' Bride, this movie tells the story of how the dispossessed 15 year old girl Chise Hatori is bought by a monstrous sorcerer named Elias. However, things are not as dire as they seem. Elias informs Chise that she has a rare magical talent, and that he will therefor take her on as his apprentice... and in the future, as his bride.