Character concept: Saga and Sola

Just going to say this up front: I have no idea what kind of kit or role would fit this character.

The idea is that Saga is a mortal man who is endowed with a magical power that causes anything he says to become true. The catch is that he is unaware of it. Now, how could he have such incredible power, and yet be completely ignorant of it? That is where Sola comes in. Sola is a celestial spirit who accompanies Saga. Her purpose is threefold.

1. To prevent Saga from learning the nature of his power.
2. To prevent others from learning the nature of his power.
3. To prevent Saga from accidentally causing a catastrophe.