The Adopted By The Darkness Ending is an ending in Prisoners of the Elder One. It is the 'romance' end for "Ebony" and "Ivory", which requires giving the Feather to them.
Erik wakes up, assuming the prior events to be a dream. However, one day he enters his apartment to see Tiffany chatting with "Ebony" and "Ivory", them claiming to be Erik's roommates. The pair turn Tiffany into a gothic lolita, and move in with Erik. While well-meaning, there is something odd about the two, which shows in earnest when they begin feeding him, mouth-to-mouth.
As months go by, Erik's body and mind changes. He feminizes, and starts wearing gothic lolita dresses. Eventually, he (now she) wakes up on the top of a building, having transformed into a lilim-like demon herself. The three sisters fly into the night, eager to hunt for their next prey.