Just for me to collect my thoughts on anything noteworthy or suspicious. I forget a lot of things in the series so this should help me keep track and anyone else who wants to look back without rereading the whole series.
Monsieur Spider's a pretty cool character. We don't know much about him but he's very mysterious and I think that's cool. Anyway, evidence he's a vamp:
Naenia staright up appears from his back. We've only seen her around cursebearers so far and it may be possible that she can just materialise around those whose names she's stolen. Idk but it's weird
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He snatched Moreau in the blink of an eye. Maybe a human could do this but it's remarkably reminiscent of when Noé carries Vani and overall just seems like a vampiric feat of strength.
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When Gano meets Ruthven after Gévaudan they are in Altus. Gano is definitely human so unless he was touching a vampire he would not have been able to get there. And what do you know Monsieur Spider was in the background during that scene. He didn't say or do anything so I'm taking his inclusion as an implication that he brought Gano with him.
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That last point is also (possibly) relevant when looking at Moreau. We don't know where he is but since he's working with Ruthven it's possible he's in Altus. He'd need a vampire to take him there. Unless dhampirs can also cross the border then Spider is almost certainly a vampire. He's also pretty tall, hard to say how tall because he doesn't appear side by side with many characters. I would guess he's similar height to Noé though. So if we meet new characters down the line who could be our mystery man we can rule out anyone short.
I don't really want to suggest this because it's an obvious theory that I've brushed off as too obvious. (Look, I don't trust Mochijun. I always feel like she's trying to misdirect me lmao). But Spider could possibly be Loki. And the more I look at random panels the more I think that's possible. But Loki does seem to care about Luca and I'd like Luca to have a good relationship with his brother.
Anyway that's all I have to say on that but while looking at panels of Spider I came across this one:
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I've never been sure to interpret it tbh. Is Monsieur Spider gritting his teeth in reaction to Noé? Is he holding himself back? Looking at it now I thought the gritting may be Spider psyching himself up for the massive jump he does in the next panel. If that is the case that's pretty interesting just because it's strange that he may struggle to make that jump. But again I don't know the correct interpretation of this.