As written, this feat has some undefined qualities and I'm interested in knowing more specific details. As of right now, I am unaware of any errata or comments from the devs' that clarify.
Deadhand StyleDeadhand Style, from Horror AdventuresHorror Adventures
Benefit(s): While using this style, if you have at least 1 point in your ki pool, you gain a +2 bonus on saves against fear effects, and the DC of Intimidate checks against you increases by 4. As a swift action, you can spend 1 point from your ki pool to empower your unarmed strikes. Creatures hit with your unarmed strikes must succeed at a Will save (DC = 10 + 1/2 your character level + your Wisdom modifier) or become shaken for a number of rounds equal to your Wisdom modifier. This is a mind-affecting fear effect.
Will hitting a creature multiple times cause an increase in severity of the fear condition? Most effects that cause fear will list specifically that they don't (such as Intimidating to demoralize), but there's also the general no stacking rule, so I'm unsure.