|Evocative Imagery, Am I right?|
Spell from the Demon Maiden in Black's Soul Sucks the soul out of whoever it touches. The Maiden in Black, who aids the demon slayers with her command of Soul power, was once one of the oldest, most dangerous demons herself.Warning, before you get all excited about this power, always ask your GM if it is OK. This is more of a mechanical curiosity than anything meant to ever be used by players. That said, maybe there is a game where this would be fine. GURPS, unlike Demon's Souls has a consistent cost for all added value, so 1 character point is objectively as valuable to a 0 point character as it is to a 1000 point character; strategically, and subjectively, they aren't equal, but they are.
Also, I need to really thank this thread and +Christopher R. Rice for their help; this is not all my own tinkering, but I want to catalog it here for future reference. Also, feel free to look at the thread, there are a lot of creative takes more suitable to other specific angles that might be more appropriate for someone given their needs and use cases.
The entire ability is two linked effects: a melee ability to reduce character point value for the victim, and increase it for the aggressor. Starting with the ability to reduce a target's Character Points, I pieced together this ability:
Soulsucker (+620%): Affliction 1 (Will; Based on different attribute, +20%; Truly Permanent, +300%; Malediction 2, +150%; Life Drain, 1d, +20%; Feature, Dice-adds, +0%; Cumulative, +400%; Sorcery, ‑15%; Melee, Range C, -30%, Takes Extra Time, 4 seconds, -20%; Accessibility, Target must be grappled, -5%) .
This will permanently reduce a target's character points by 1d. Life Drain is explained in the thread mentioned earlier as a cosmically enhanced version of add a character point worth of disadvantages, the cosmic enhancement being any disadvantage. Earlier in the thread it is calculated at +200%, but I believe that a later comment mentioning it should be 20% is actually correct.
A tiny variation on this ability is to replace truly permanent with normal permanent, and cosmic, cannot be healed with regular magic to make a still dangerous ability, but one that can be healed through abilities that remove curses. This costs 62 points because that combination is 100% less worth of enhancements.
The more controversial element of this ability is the reverse, that gives the same value in character points. The above ability might be almost OK for a very evil PC by itself if used against NPCs, but this one is the bridge too far.
Soulsucker : Linked Effect to add Character Points (+800%): Affliction 1 (Will; Based on different attribute, +20%; Truly Permanent, +300%; Malediction 2, +150%; Life Sink, 4, +200%; Feature, Dice-adds, Character Points added are equal to the roll for the first part of the spell, Self Only, +0%; Cumulative, +400%; Mana Sensitive, -10%; Link +10%) 
Life Sink is the reverse of Life Drain and adds a character point per each level. It is basically the parent ability in reverse.