From Edge of Darkness Wiki
Hollow Soul
Your character can be possessed even by spirits that cannot normally use the Possession Numen. All the spirit needs to do is fetter to the character, and then it can possess him for a scene with a contested Power + Finesse versus
Resolve + Composure roll. The character can serve as a mouthpiece for spirits too weak to normally interact with the material world on a meaningful level, but also gets sought out by more powerful spirits who would prefer to abuse the character’s ability.