12. I think it might have been intentional just to spite his publishers, since he just wanted it to be a shounen manga, unlike his previous works, and his publishers were the ones who wanted the manga the way it was initially. Oh, and a few other characters are expy's of characters from his previous works. I think Nodoka fits the bill as being an expy of Shinobu, and Asuna an expy of Naru, from Love Hina. I've been too busy to determine if any other characters are borrowed from his works prior to Love Hina.