One evidence is this.
Spoiler (mouse over to view)
She said that he blushed when he met her eye BUT Hanai is right beside her so he could have blushed when Natsukasa saw Hanai, not Naedoko.
If so, I wonder if it'd be brought up later on into the manga. Maybe like everyone is asking who their first love/crush is, and Naedoko would say Natsukasa.
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"Shouldn't be alive but the condom broke."