User blog comment:B214/Question and Answers/@comment-24098614-20131216060806/@comment-1359322-20131216062941

That depends on who they reincarnate as their servant, just randomly reincarnating Devils are pointless, it could create some scenarios such as the servants' abilities are opposite of each other thus making the team weaker instead.

As to the Devils reaching Ultimate-class, tor Devils that reaches Ultimate-class, they get additional fame and extra territory for themselves.