Thats a Dark Eldar, or Drukhari. You know, the space elves that went so incredibly, interstellar, ballistic with sex and torture that they, uknowingly, created the chaos god Slaanesh which started with this big ass psychic explosion that killed a lot of Eldars. And i mean a lot!
Isn't Drukhari's whole thing is that they fully embrace the tenents of Slaanesh - over the more reserved and secretive Eldar cousins after their great empire collapsed with their excess birthing a chaos god?
If I recall, Drukhari survive by extracting the very essence of another creature's most tormented pain, agony or whatever qualifies as excess.
So they would go out of their way to extract it through cruelty, abuse, torture or whatever achieves the desired response they are looking for and push a person to the extremes into a state that you wish you were dead and then push even further keeping you there on the fine edge to get their fill then, then dispose of the husk once it served it purpose or they got bored with their "toy".
I am only have a passing interest in the universe so I am opened to be corrected on any point if I missed something or misinterpreted