It's Imouto-chan from an alternate universe where time runs differently/she's the older sibling/whatever.
Imagine that that's already been revealed to be the case, then go back and read exactly how Kyon describes how she seems familiar to him when he's talking to her over the phone, and tell me it doesn't seem like an obvious foreshadowing...
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FGO Info: (JP) 055835281 | クワイガンケニー ==== (EN) 952525630 | quigonkenny
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