WAIT I HAVE A NEW THEORY, in the MC's cell phone photo, Himawari appears with darker hair, but now it seems to be a lighter hair color almost as if she were blonde. Himawari has light brown hair but I don't think it's a coloring error.
CHAPTER 5 PAGE 22, it is clearly seen that even in childhood the hair is left white, but in the photo it is not left white. I repeat, I don't think it's a coloring error.
It MUST be a clue.
What other character have we seen that has that color tone hair, so that the coloring is like that?.......
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UESHI
She has reddish hair, that in coloring it is never left white.
WHAT IF Ueshi is the original childhood friend and somehow Himawari inserted herself into their lives by kicking Ueshi out?
Ueshi doesn't loop, she's a victim of Himawari's wishes, that much can be confirmed.
The question is how and why it happens... But it's all related to the childhood incident.
Edit: I forgot to mention that perhaps Himawari doesn't remember because that incident isn't part of her childhood memories, but rather a memory that happens before she self inserted as their childhood friend. As for why Ueshi doesn't know them as childhood friends, I have no basis for that, but in these kinds of stories, it always happens that they forget they knew each other in childhood and only remember much later.
That's all I have for now