If Mia wrote a book, it would likely be a biography on Ghaleon in the hopes that someone besides herself remembers that, hero or villain, he was first and foremost a man. Unfortunately, most people who would be good sources of information on Ghaleon have passed long ago, as Ghaleon was nearing the teenage years while Mia's grandmother was a small child (at least according to the manga 'verse), or no longer have many memories of him. She'll have to dig in the Magic Guild's records and diaries if she really wants to write such a book.