I, personally, would like to see each girl get her own unique mechanic rather than just duplicating Rogue's addiction system.
I dislike this idea greatly, I don't like arbitrary mechanics which IMHO giving each girl a custom mechanic without good reason is, each girl having a custom mechanic is untenable long term as more characters get added and annoying short term as it result in inconsistency, why is it different for each girl? "just cause variety" is not satisfactory imho.
I would prefer that the addiction mechanic be tied into Zeros power so as to have it make sense across all girls, Zero's powers could be chemical in nature so that Zero's body fluids are the vector by which it spreads, skin contact works because of skin oils carry the power blocker and different body chemicals could be more or less potent.
Something like, Blood > Semen > Saliva > Sweat > Skin Oil > Pheromones/Airborne
The addiction quality can be linked to the chemical nature of Zero's power allowing levelling up to be expanded into a skill/power tree.
Rather then just power nullification and addiction the chemical nature of Zero's power would allow for the game to hit some other tropes as well, each of which would be its own branch on the skill tree with up grades/potency levels allowing the player to choose how their version of Zero operates.
The potential branches that I see are,
Nullification -
Addiction -
Love -
Obedience -
Inhibition -
Lust -
Edit: Actually I can think of potentially unique mechanic for girls, each girls has her own weak point, Rogue's is simple touch, Kitty's is Restraint/bondage, Laura's is Danger/rougeness, Emma's is mystery/surprises, Mystique's is her real form etc, keep the addiction but make what get though their "mental shield" is unique.