The Devouring Forest is one of the most well-known spots to get rid of the suicidal or unwanted: the children nobody wants to take care of, elderly, sick, injured.
Kassja is ill, and being too weak to birth children or work her village throws her into the forest. Yet, as she is dying under the scorching sun that trespasses the greenery, the spirit patron hears her hateful prayer of death for those who used to be her folk. It resurrects her, green parts merging with her now healed body.
The patron lets her live under one condition: she will be faithful to it and will help it destroy humanity in the region.
She accepts the deal.