We see him at Abby's capture, but we don't see him at the sacrifice, only the Magistrate guards.
Seris is an interesting "topic". In the trailer it is said that the Void was hungered for a body, then the Abyss was unleashed, and everything was destroyed. And about the lore note, I don't like to say that, but that is a disaster for me. Half of it is there only to explain her abilities. The teleporting and the sou collecting are okay, but the wibly wobly timey wimey is just not. More and more paradox, and makes her op lore-vise. And the healing is not consistent with the Abyss, bevause that is the tipe of deity that kill everyone who is useless, and don't bother with healing. So if I were there, I would rewrote that part (not the origin one, that is cool).
And for the origin: In my theory, when the Void possessed Abby, and the village was destroyed, the portal to the Abyss was closed. Everybody died there, except Seris, who woke up with full amnesia, and the first thing that she saw was the welcome table of the village (i think it was a town). She knows nothing about herself, so she wanders all over the realm. And while there is the pert of the void inside her, her body is not her puppet. She is an individual person, "made" by the void. A bit similar to Vision, who was a part of Ultron and JARVIS, but actually neither of them. So now she wanders and tries to discover her past and herself.