:that absorbed demonic energy through headpats
Absolutrix does this only work when targeting demons? Normally succubi/incubi prey on humans, but normal humans would not have demonic energy. Instead, a demon would prey upon life force energy or vital energy.
Codified in GURPS terms, the necessity of only being able to touch with 1 hand is Sense-Based (Reversed) for sense of touch. Only being able to target a specific hit location isn't something I have seen codified yet. The skull is normally -7 to hit, presuming this is the only part of the head you can pat, since it is normally done on the top. The face is only -5 to hit so if that would also work it would be less limiting.
Since headpats work even if you only touch hair instead of skin I don't think the Contact Agent limitation would be used. However since there is "Blood Agent, Reversed" there should probably also be a "Contact Agent, Reversed" if you must touch their hair (or hat) with a bare hand.
Poor wording, I meant "Generates demonic energy by draining regular energy from humans through touch". It could be anywhere, I just figured the irony would be funny if the aliens chose to choose heads and hands only due to their culture.