Oh shit I didn’t even think about that. I kinda read it straight forward in that he had been drugged or something and had repressed trauma from Ms. Nakama and he ended up forgetting things. But, the other way around where she was trying to help him makes sense too. In fact it makes more sense, adding the extra detail of their names is interesting as well.
Just to add onto how I believe this theory now. It isn’t totally unrealistic for him to finally break and remember that incident but the teacher’s lack of reaction to him fighting back and the fact that he didn’t remember any repressed memory while in the situation makes me think Ms. Nakama was trying to help him. Although lady you could get him to a doctor or something lol it looks like he has some sort of psychological thing going on if his memory is that bad lol. Aaaa I love stories that give you the room to draw your own conclusions
Fukano was sexually abused by Nakama-sensei. she wasn't trying to help him, she systematically abused him. That's why he used to forget everything: from writing own name to his interactions with Nakama-sensei. when the abuse stopped, he got his memory back.
We often forget the things we did in the past, especially during our infancy and childhood. It's perfectly normal and most of them are shallow. In the translator's notes, Fukano's friend's name means shallow field and I think he represents those details in our childhood that seem ordinary. Fukano, on the other hand, experienced something traumatic with Ms. Nakama, hence his name meaning deep field. Traumatic experiences are often, if not, always ingrained into someone's memory regardless of age. They hold a huge part in someone's important memories. People may move on from them, but they won't forget.
Regarding Ms. Nakama's name, I think her role was to help Fukano remember things by letting him experience something he won't forget, hence being a "friend" to him.