The Will skill represents your character’s general level of mental fortitude, the same way that Physique represents your physical fortitude.
Special: The Will skill gives you additional mental stress boxes or consequence slots. Average (+ 1) or Fair (+ 2) gives you a 3 point stress box. Good (+ 3) or Great (+ 4) gives you a 3 point and a 4 point stress box. Superb (+ 5) and above give you an additional mild consequence slot along with the additional stress boxes. This slot can only be used for mental harm.