The Dark Side is said to have a hunger as well as a malice to it, and these are traits that resonate strongly with certain individuals. Those who find themselves exploring their innate affinities can learn the profane techniques by which a target may be drained of its energy, sometimes fatally so.
No Points: Your ability is limited by your fledgling understanding. To attempt a Drain you must be undisturbed and allowed to concentrate. You're unlikely to kill anyone not already close to death's door with just this, but you can sap them of strength and stamina.
1 Point: You've harnessed your own hunger, and learned to weaponize it. You have learned how to drain the target of their stamina and vitality though you still need some space, and to be unharried by any immediate threats.
2 Points: Each morsel you have managed to rip from the unwilling so far has only served to further whet your appetite. You can now seamlessly weave your draining techniques even in the midst of pitched battle, or target several in an area when not immediately in danger of retribution. You've also discovered how to use this stolen energy to bolster your power on the attack.
3 Points: Your hunger ever gnaws at you, and ever you seek to satiate it. You can drain the essence of many simultaneously by creating deadly fields saturated by the Dark Side, withering most anyone caught within. You can then use this stolen energy to empower yourself and your other Force-based attacks.
3☆ (Mastery): The ultimate refinement, or degradation, depending on your point of view. There's little left of the person you once were as slowly but inexorably you become consumed by your own hunger. Your very presence is enough to sap the life force of those not trained to resist such things, and you need that energy just to sustain yourself until the next feast. The purity of your ideal is plain for all to see.