[quote=@vancexentan]
[@Sublimation]the only thing I can say is that Caster could be taken over but he's already made and you'd have to play as that specific character as all the other spots are filled to my knowledge. 
[/quote]

Ah okay so I can't make a new servant to replace the current caster. Well, I'll be waiting around and will likely be available in case you need someone.