Symbaresh Twinsouls are warriors (usually ex-myrmidesh) of the Slaanesh Sybarites that, chafing amongst being one amongst the faceless many, took the shortcut to power and allowed themself to be possessed by a daemon of Slaanesh - this is achieved through ritualistically marking their bodies with runes of conjugation and offering up the souls of six aelves.
However, although this arrangement offers the Twinsouls phenomenal speed and strength, it also leads them to exhibit a curious lack of self-awareness over time – perhaps speaking only in third person, or remaining oblivious to the most grievous of wounds. Through these cracks the daemon attempts to wrest control. Though the strongest-willed Symbaresh (known as Egopomps) may successfully subsume their patron and take their power without paying the cost, most are eventually overwhelmed – reduced to wretched soul-slivers trapped in their own bodies. [1a]
Taking up weapons of their own choosing and discarding their helms (the better to draw the Dark Prince’s gaze) they gleefully forgo the mono-obsessive techniques of their blade-cult in favour of displaying their own inventive skills. These egomaniacs constantly compete against one another to perform the most impressive feats in battle, shrieking rhapsodies of self-praise all the while. [1a]