Nice idea. I found the anime mixed a fair element of soft-porn with just enough storyline to make it enjoyable.
I loved the role of Maria Magdalen Teresa (because she has awesome dress sense!) so would like to play a character like her, a supporting role or partner to a qwaser. Definitely the Athos side for me.
Also happy to play a student, someone busty and a bit dim or moe-like, such as Tomo.
BTW it would be very simple to make it so that a female qwaser cannot gain power from her own soma, but must feed from another maiden. That way you don't need to restrict the physical shape of the female qwasers.