Soul-bound

The soul of this creature is bound to a higher power or being, in return for a measure of protection.
When this trait is first gained, the entity to which the soul is bound must be decided. Many Imperial psykers, especially Astropaths, are soul bound to the Emperor, for example, whereas Chaos Sorcerers may be bound to one of the Ruinous Powers.
A soul bound Psyker rolls an extra die when forced to roll on Table 6–3: Perils of the Warp, then replaces either the ones die or the tens die with the extra die he rolled to determine the final result.
Upon becoming soul-bound, the Psyker must choose one of the following effects: 3d10 Insanity points, the permanent loss of his sight, permanent loss of 1d10 points from one characteristic, or a random mutation. In addition, a soul bound character is permanently indebted to the entity, which undoubtedly entails all manner of other duties and consequences.