Witch War After a Kiss

One day, Nadeshiko Aoi, a slightly geeky high school girl, meets a beautiful boy. He has a mysterious atmosphere, and he makes a proposal that Nadeshiko has never thought of before. Asking if she wants to know about her sister, who went missing two years ago. Of course, Nadeshiko wants to find out where her sister is, so she listens to his proposal, and in exchange, for information about her sister is that she make a contract with the devil and become a witch! In addition, the witch has a mission to participate in a "War"... What is Nadeshiko's fate as she gets caught up in this battle of conflicting agendas?