So the woman is a pedo? And a biting one too. She's "hungry".
And I wonder if the classmate didn't go through the same thing, seeing as she seemed troubled to see them together. So her strike zone is pretty narrow: young teens.
I don't see where this is going. Creepy or romantic?
Oh, I just understood the Cicadas metaphor. "They are transient". Like the time before the young girls become adult. Ie, that woman loves young girls in the period of time when they are no longer children, but before they become adult.
Oh! The blood drinking and her costume gave Kousaka-san away. She's a youkai known as a Hinoenma or Enshoujo, a female vampiric seducer that drains men of their blood and ki to maintain their youth and beauty. They are depicted as young maidens wearing traditional clothes and an umbrella, and reside in remote villages and farm houses. And they have a hidden pair of wings. The difference here is that Kousaka-san prefers young girls rather than guys.