La Pucelle Tactics (EC MC)

Okay, this is by far one of my most favorite PS2 games ever, however, the US got the worst version of it, but I'm not bitter... Well, of course I am, but at least I got to play it. Anyway, the main heroine is Prier(aka Priere), a hot tempered nun. If you go to the Dark World with her enough you'll get a scene where the demons bestow the title Demon Lord upon her, and then a ending with her becoming a (reluctant) Demon Overlord. It's more humorous than anything, but still, it is a good character(a nun no less), becoming a Demon Overlord. She even makes appearances in other games in this form, AND in a remake of the game(La Pucelle Ragnarok) there is a path where you can play as her Demon Overlord self, so as far as I'm concerned it's canon.
For more info, see here
http://disgaea.wikia.com/wiki/Priere

Becoming a Demon Lord


Becoming a Demon Overlord


There's also a succubus species by the name of Lilith(one of the two female monsters in the game not counting the butterfly girl party member Papillon) who can cast a spell that charms called Sultry Scent. Unfortunately, I could not find video of this, but here's what she looks like
http://www.succubus.net/wiki/Succubus_(La_Pucelle)

Finally, if that wasn't enough, there is also a Dark Persona for one of the character, which is somewhat relevant to EC so I'm including it.
Regular
Dark(with additional info)