Ha! My dunce brain thought it was little Yumi, given they used to hang out and Kaori is older than her and the clothing color scheme but yeah, the eye is Kaori's, strange. Those are Sekai's butterflies too aren't they... stranger still.
Edit:
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Actually, checking Yumi's eyes... they're not so different to that little girl's that it it couldn't just be lighting differences could it?
Edit 2: Although the kid is wearing the same gloves Kaori wears... it's probably Kaori, ignore me.