Can somebody pls tell me I'm lil bit confused...in those flash back scenes in 2016, she knew him...but later she…
He started using the comb some time later I mean after some years when the started getting even more close. He kind of erased himself off. And why she remembers that song is because it was taught by her grandma and has nothing to do with him. He can even listen to her without that song. But with that song he gets called specifically. Also, she started getting her memories with him back when she saw him again according to her for the first time. And then she got reminded that she already knows him and thereby the song.
So, the synopsis is not the only thing similar but also the hairstyle of the teacher from chugakusei nikki. Umm differences though are that he is a mathematical genius which can offer a very interesting plot if used well. Looking forward to it.