So Shadow, I need someone to be Sanae's friend, someone that told her to come here but very purposely didn't tell her anything about what would happen.  Think Zitka would be evil enough for that?<br/><br/>As for servants, they can change throughout the game without problems, although once someone starts a duel, all their servants are "locked in".  Also, nothing prevents a servant from initiating their own duels, having their own servants, etc.