(There may be spoilers for both shows. You've been warned.)
Even after the evil one was defeated, madness still remains in every shadow. Nobody bothered to check, it never crossed anyone's mind. Everyone assumed that when he was destroyed, the madness would be too. No one even knew it existed until the young witch Sakuya, magic theme being the Owl, discovered it. She used it to her advantage, hoping to avenge the witches who had been killed by the DWMA's students. When she realizes the potential of crossing magic and madness, things get a bit mixed up.