Alright, fuck off with the "meddling ex from the distant past" trope. It's played out and obnoxious.
We all know how this is gonna go. Even though he's vying for the affection of his students, he's gonna hold Rinko to a double standard. He's gonna try and blackmail her into dating him, and Arase's gonna show up just in time to say "I'm a below average student who gets tutored by Ms. Rinko, that's it. We're not dating, so Rinko-san isn't doing anything wrong."
And then the Hot Blonde is gonna show up and roundhouse kick him right out of my fluffy age-gap romcom.