You are Edelgard's daughter, the princess of Adrestia. You have already been victim of blood experiments causing you to bear 2 crests. This was all Rhea needed to bring Sothis back completely. She approaches you with the goddess's heart in her hands.

It'll only hurt a little.

she replaces your heart with the goddess's heart, you can feel an intense pain so intense that you fall unconscious, when you wake back up, you're in the infirmary of gareg mach. You fear this woman that you thought you could trust. And you have a third crest, the crest of flames