Nyarlathotep Is an ancient deity that has gone by many names; The black pharoah, the crawling chaos, etc. He seeks to bring himself into this world, but cannot due to an ancient barrier that prevents gods from crossing over. For his plan to work, Narly must be born as a child, who would serve as his avatar. This avatar would serve as a Dark Messiah, one who would bring ruin and chaos to the world. The person selected must be a virgin who is also infertile, unable to have children naturally.
In ancient religious texts, virginity was highly prized as a symbol of purity. Mary was free of original sin, and the only candidate for the mother of Jesus. This is also a running theme in other works of folklore, with purity being linked to individuals worthy of note. Virginity meant being untainted or spoilt by the ways of man, which provides the resultant being with a certain specialness within a culture.
However, Narly is a being of chaos and instability, associated with physical and mental corruption. Looking upon it's true form would bring about insanity and mutation. A being such as this would have little relation to concepts such as "purity" for its very essence causes chaos and disunity. It shouldn't matter if the individual was a saintly mother Teresa or Kim Kardashian like figure.
How can I link this thrope to an Eldritch being in a way that makes "purity" a requirement for him to cross over?