The word succubus appears in Declan Marsden's research files alongside incubus, in the demonological context of cambion origins. Both terms bleed from the page half-Latin, half-menace, carved into margins alongside symbols and hand-drawn figures. In the traditional framework the terms describe, a succubus is a demonic entity that assumes female form — a counterpart to the incubus, the two forming the dual mechanism by which, in scholastic demonology, demonic entities could mediate human reproduction for their own ends.
In the saga's specific mechanics, the figure who functions closest to the classical succubus framework is Agrat bat Mahlat — not because she seduced in the classical sense, but because she acted as broker and intermediary, preparing the vessel and opening the crossing. She is the key, not the occupant. The succubus tradition names the general category; Agrat bat Mahlat is the specific instrument deployed within it.