This is what your defenses look like
Whenever the character is the subject of any supernatural power that seeks to transform, infect, taint, transport, or control her body or spirit, she may reflexively spend 1 Essence or 1 Willpower and roll Willpower against difficulty 7.
Motes are not inherently part of your soul, they are something you keep in your soul, but looking at the base charm from 2E:
The Sun's Chosen define their own reality. This Charm perfectly protects the character from any Shaping effect that directly alters her mind, body, spirit, possessions, or Traits.
It does cover possessions. One moment, editing.
Edit: Done and they revealed another charm, specifically one that binds you in place with soul-steel chains which cannot be broken only dodged or parried when they hit you. After that you have to take the penalty, though it does go away on its own in three rounds.