"Ferried from an unknown time and place, a haunting presence has been detected. We must now confront the ancient threat growing at our doorstep"
Either the Witness is using the Vex on Neomuna to bring back one of his Disciples or the Disciple is a Vex from the Sol Divisive.
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Vex are like hive minds, forming one into a disciple is, to my mind, probably not worth the effort. Make them into followers sure, but I doubt you can go any further with them.