A more precise use of the word is that Nanasawa is an ebophile and a predator,
No, she’s not. She would be, if this were a situation in real life and time travel were not involved, but at that point you’ve stopped discussing the story (and hence are technically off-topic for this forum).
As I said before, Nanasawa is both older and younger than Seto, and has just met her and has known her for many years. She’s not attracted to Seto just because she’s young; she’s attracted to her because she’s Seto, who she’s been in love with for over a decade.
The only way to make the terms you’re tossing around applicable is to ignore the basic premises of the story.
That's true but she is still being kind of a creep, touching a high school girl, even if she has been in love with her for years. Like, if she was still in present day, she would definitely not do that to the present Seto (because of her lack of confidence). It's even weirder if you think about how the past Seto knows nothing about older Nanasawa, who is touching and kissing her out of no where. She clearly takes advantage of the age gap and "onee-san" lead as she calls it. Maybe not pedo, but she is definitely predatory, that's for sure. I don't hate the story for this, it's just fiction, but I will admit it does urk me a bit. I suppose this story is just plot with a side of ecchi.