Curate, connect, and discover
The way this makes so much sense
okay agatha all along episode 6 spoilers and also possibly absurdly outlandish theory incoming
i have a theory about lilia putting the sigil on billy. i assume she put it on him because she saw something that would endanger him if everyone immediately knew who he was and i initially foolishly assumed she was referring to agatha because you know. agatha is mildly unhinged after all
but I'm starting to think it's rio....because there's the theory going around that rio is death personified and honestly it makes so much sense. she can't kill agatha because death can't Kill others, it can only come when it's called. her power would kill agatha because it's a death domain power and either it's innate to her and only she can handle it, or you can only earn death related abilities a certain way. (also she's THE green witch. ashes to ashes and dust to dust etc every body returns to the earth)
in episode 5 she mentions that she hates ghosts which makes sense because she'd see them as perverting the natural cycle and clinging onto a semblance of life after death. so what on earth do we think rio would do if she knew that Billy's soul was possessing someone who's supposed to be dead? somehow i don't think it'll be pretty.
the sigil breaks at a weirdly specific point, too. it's after agatha kills alice, which means that rio is going to be preoccupied for a little while at least, giving billy and Agatha some time to discuss things. and if rio is death then agatha is likely the only person who knows that, and if we're getting technical the sigil only breaks once AGATHA concretely puts together that teen is billy.
lilia's divination works VERY weirdly, she's all out of time and often doesn't seem to remember her premonitions, but I would bet that the sigil was created with the knowledge that it would be broken once agatha specifically was the one to put the pieces together. because agatha knows rio and therefore she knows death. and we've seen already that agatha is VERY emotionally intuitive, it's what makes her so good at being a dickhead to others because she reads tells and emotional wounds so easily and knows exactly when she's hit a nerve. so i wouldn't put it past her to know Rio thoroughly enough to be the one to keep billy safe from her.
i just think the timing of the reveal is all very coincidental. not like, bad writing or anything, but the fact that agatha figures out it's billy AND has a whole emotional reunion with him with every other member of the coven missing feels a lot like Fate (which would probably come under lilia's domain). because now agatha and billy have an understanding of each other that will make it easier for them to walk the road together, but ALSO, nobody else knows. and agatha, who knows that rio is death and knows how rio feels about breaking the life-death cycle, can keep it a secret for him. she can protect him, even if he doesn't trust her.
anyway theory over but i swear to god billy and agatha better have the most lovely found family story arc. billy claims he doesn't need agatha but agatha has already adopted him in wanda's stead because she remembers being angry at the world like he is. oh and also she knows he does need her because death could be after him now lol