Something that I think is underrated in the fandom is the concept of the cattle children making friends their age in the human world post-canon. I like to think that the younger kids would have an easier time socializing while the older kids may be more withdrawn (especially with the adults), but get better with time.
Do you have any headcanons about their interactions with the human world? And where in the world do you think they settled down at? I’m guessing that snowy area Alex lived at may be what was formerly Russia/East Europe because of his last name, but idk.
I also find it odd that Shirai never told us what Emma’s ‘new’ name was (that becomes her middle name). Have any in mind?
I don't know if I'd say underrated? If asked I think a lot of fans are open to it/enjoy it, myself included.
Underexplored though, definitely, but I think this stems from how hard it can be to sell original characters in fanfiction the closer in proximity and importance they are to the main characters. This is also part of the reason I believe Matilda is Norman's biological mother and Sienna is Emma's biological mother are decently popular theories: it offers people the convenience of already having a minor canon character with a design and foundations of personality and history that can be referenced with greater recognition among other fans to project headcanons onto.
But if we're just talking about alluding to it happening in the background, one of my favorite Rayemma fanfics, She Loves Me, She Loves Me Not by groundedreamer, touches upon it in almost the exact way you describe:
I didn't even realize it was a Rayemma fic at first (or a Hanahaki AU; I usually don't read those) because I zeroed in on it being in the Jemima tag with the entire first chapter being dedicated to Ray & Jemima bonding.
Highly recommend if one's open to RE.
Do you have any headcanons about their interactions with the human world?
This is very broad and we could be here for a while, but all the cattle children aware of the truth before crossing over to the human world, including the Grace Field children who didn't escape but saw Isabella being murdered, have PTSD. This initially makes it rough for the older children to accept help from healthcare professionals and to navigate the best way to handle things for the younger children.
I'm always going to advocate for Norman and Ray going antiquing or to junk shops for items they can fix up and potentially gift to people, especially if they end up finding a duplicate of the music box Isabella gave Emma on her sixth birthday.
(Mystic Code Book Chapter 1 Q&A | Questionnaire Translation Source)
I also talk about my preferred career paths for the trio here since I'm not fond of the path Shirai took with Norman and Ray, even if I understand why he did it. (I am 100% behind Nat becoming a famous pianist though.)
And where in the world do you think they settled down at? I’m guessing that snowy area Alex lived at may be what was formerly Russia/East Europe because of his last name, but idk.
I agree given that they start out in former New York City that the demon god would send her to the opposite side of the globe. And while Alex is fluent in English, I think it's sweet if the kids learn Russian to speak with him as he becomes integrated into the family as a father/grandfather figure.
I also find it odd that Shirai never told us what Emma’s ‘new’ name was (that becomes her middle name). Have any in mind?
With how cagey he was about confirming what a number of people had already suspected about Ray's bait note because he wanted to leave the door open for multiple possibilities prior to his health deteriorating, this doesn't really surprise me kfjdgvkj
I default to Wendy because of the Peter Pan connection, but I also gravitate a bit to Alice, Charlotte, or Jane.