Anyway, if we have to look for clues, I guess it would be in the Tanabata theme.
It all points to the summer triangle (vega deneb altair) and the legend of Hikoboshi and Orihime. Also, Tanabata literally means "the seventh evening of the seventh month"
Tanabata always falls seven days after the New Moon at the end of seven full lunar cycles.
Aya reappeared after seven years.
Etc, etc. The number 7 is particularly important in the Tanabata myth.
Maybe Aya and Koto are Orihime and Hikoboshi and the one separating them/keeping Aya from coming was Erika (did Erika confess loving one of them? It's still unclear).
But they're reunited after a 7 years cycle because fate wouldn't allow it.