From Destinypedia, the Destiny wiki
Styx is an Vex domain located deep within the The Nexus. It channels a river of Vex code to maintain the Endless Night through the flow of directives. The domain is governed by the powerful Oppressive Mind named Dikast.
The domain collapsed following the defeat of the Mind, however a Taken incursion infected the domain and prevented its destruction. The Oppressive Mind was reborn with corruption by the weaver, Quria, Blade Transform.