Ananke's sister is a mysterious figure who appears to have a hand in the development of the Recurrence. Her name is unknown.
Ananke's sister lived 6000 years ago and was present at the first Recurrence. She was an old woman and had a grandson, who she encouraged to leave her so as to keep him away from Ananke. She and Ananke appear to have orchestrated the Recurrence together, and in one final meeting between them they established a set of rules to govern future Recurrences.
The first rule, established by Ananke, laid out the roles of the two women: Ananke as maiden, the sister as mother, and Ananke as crone. The second rule, established by the sister, was that there must always be twelve gods, and they all must be gone by the end of the Recurrence, including Ananke. The third rule, established by Ananke, was that she got to choose which gods make an appearance. The sister agreed, but decreed that her god should always be among them. Ananke responded that this god would awaken last. With the terms seemingly established, Ananke killed her sister, but not before the sister croaked out "And...four...".
It is not clear which mythological figure Ananke's sister represents, but she did refer to her dealings with Ananke as "the dance of desire and necessity", which would appear to indicate that she represents desire.
Signs may point to the fact that Persephone was the god that she represented and that would be incarnated last, which means that a Persephone has been present for all the Recurrences. This could mean that either Persephone was hidden by Ananke, or had her head removed immediately upon each of her incarnations, as Ananke attempted to do when she was incarnated in the body of Laura Wilson. A Persephone appeared during the 1920s Recurrence and had her head removed prior to or during the events on Lucifer's Island, her identity unrevealed to the other gods.