Working out the kinks (hah!) of this idea yet, so bear with me. Think I have enough of an idea though to post. Perhaps a prospective partner can help flesh it out more firmly.
This story would feature two famed, and fallen women from myth: Lilith and Lamia. Both having long been damned to the Abyss they've earned their stripes so-to-speak and each oversees their own host of succubi. In the hierarchy of the Abyss they are Greater Succubi, the only two of their kind. They 'compete', in a way, in that they strive to outdo one another, dispatching their succubi to dole out evil deeds of seduction.
The goal, or one of the goals is to bring these two together for a liaison. Another option, and or side plot could be the seduction of Catholic nuns, ones who lesbian impulses lie dormant, requiring a nudge to bring up to the surface. Also, a greater demon could be manipulating them, egging them on to coerce them into a coupling of the two succubi.
Both myths of Lilith and Lamia have references to them ultimately becoming succubi. Sometimes the two are conflated, but for the purposes of this story they are two different entities. They each also affiliated or associated with serpents or serpentine characteristics. Something we can play up if so desired.
Pretty open to working with someone on the finer details. Only thing I would hold fast on is that they are Greater Succubi, and each has their own distinct background.Backgroundhttp://en.wikipedia.org/wiki/Lilithhttp://en.wikipedia.org/wiki/Lamia_(mythology)