Talk:Succubus/@comment-201.230.251.222-20140624211734/@comment-203.210.0.63-20140819012156

A mix of both.

When you become a incubus, you can live with just the mana your wife provides you, and she lives on your vigor, which now you'll be generating a lot more than when you were human. That's why the canon entry has it that couples could last through the winter by staying home and do nothing other than copulating endlessly.

More vigor, more mana; more mana, more vigor. That's why those monster girls who copulate a lot with their husbands will become very powerful.