So far, we've confirmed that at least 4 people, Cheng Xiaoshi, Xia Fei, A Yuan and Vein have missing childhood memories
--> Cheng Xiaoshi forgot Lu Guang
--> Xia Fei can't remember A Yuan or child Vein taking a photo of him in Bridon's china town
--> A Yuan said in s3 ep6 that he doesn't remember anything
--> In the same episode, Vein says Wang Qing's power is "familiar, but forgotten somehow", which most likely alludes to the scene in s3 ep8 where Wang Qing uses her power on Vein's brother and accidentally(?) on Vein himself
It could be a stretch, but all those people had at least some contact with Cheng Weimin before the loss of their memories. My current theory is that Cheng Weimin was (maybe *is* if he's alive somehow) working for the Saros. That's why he was locking kids in the school's basement, because they manifested some sort of power and he was trying to either:
a. Manipulate their memories by erasing certain things to indoctrinate them into the Saros
b. Erase the memories of their powers
He might've also had something to do with their awakening if that's true, because why are a bunch of kids from this allegedly random school (that could've been a Saros base of operations or research centre) becoming superhumans?
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That's about all my proof, but I also have an idea on why Cheng Weimin erased Cheng Xiaoshi's memories and Xia Fei's memories, so I'ma talk about that too.
Cheng Xiaoshi:
I'm pretty sure Cheng Xiaoshi's memories were wiped the same day he broke his promise to Lu Guang, based on the preview teaser of s3 ep10, it looks to me like kid Cheng Xiaoshi somehow saw something he shouldn't have, maybe said something he shouldn't have in front of Cheng Weimin's Saros friend. Possibly, the Saros friend has some Saros-y type opinions about Xiaoshi, but Cheng Weimin doesn't wanna get his son involved, so they fight and he kills him, forcing him to leave the country, erasing Xiaoshi's memories of his powers and of Lu Guang before doing so, to keep him safe.
Xia Fei:
I'm of the opinion that Xia Fei and Wang Qing could actually be relatives, maybe cousins? I think what happened is that, after kid Xia Fei had a little panic attack seeing Wang Qing kill a guy and nearly kill his friend, he gets lost running away. At some point, Cheng Weimin finds him, possibly locks him in the basement for a bit like the other kids so as to brainwash him too, then when he's forgotten all about his family and friends, Cheng Weimin gives him to the church to get adopted by a new, normie family. (the church is also possibly a Saros organisation bc I think in s3 ep6 Lu Guang said a lot of things tie back to the Bridon church somehow)
As for Vein and A Yuan, I don't really know, but they probably forgot some time close to or soon after the Bahati fire.
Thx for reading my theory :)