Actually, if I remember correctly, Vampirella does NOT need to feed on/prey on human blood at all. She's a rare 'breed' in that regard.
Morrigan is supposed to be a succubus, though, aside from her appearence & some suggestive quotes, you could hardly tell, by how she behaves in the 'DarkStalker' games. She's more warrior than seductive, LOL! (I know: she's from a Fighting Game).
Technically Morrigan does act very seductive in games, she has some of the sleeziest(if not THE sleeziest) moves of all Capcom characters including a bed behind the curtains move and her younger self tied you into a domintrix puppet show. Also, her ending in the first game has her kiss someone after kicking their butt, then draining all the life out of them leaving them just bones.
Besides these two girls have good reason to be aggressive rivals and forced-together allies: Both are fighting Vampire(s) because of their own family lines past involvement with the beasties.
Besides, why ELSE would they pull on each other's hair, lock up in a graveyard,then work out their differences(olny momentarily we assure you) towhup on some peeping tom Vampire's butt? ? Its not like their drop dead freaking sexi
There was a bad movie called "vampirella", I'm no comic buff, but I understand the movie was pretty much crap. Google or Wikipedia if you want more info on Vampirella, if you want pics on either girl DA has thousands, literally.