This Pixie is a tricky demon to get along with, so I'll give you some tips! To negotiate, one needs to offer a demon some money (called Macca,) an item, or even a demon (in your party's) life to get things started. Don't give away too much, though, cus the demon might see you as a pushover! Then, you need to talk, and try to win the demon over to your side. Simple as that!