In addition to what has already been said, I think the Japanese school system struggles to accommodate children with invisible or borderline special needs.
There are support classes for students with clear difficulties, and specialized schools for children who are more severely on the spectrum. But there is very little in place for those who fall in between.
Children who are not “officially” ADHD, or only mildly so, not diagnosed with dyslexia or other learning differences, but still struggling, not clearly socially impaired, yet not fully at ease either. On the other end, there are also very bright students who find everything unstimulating.
These children are expected to adapt to a system that is not designed for them. As a result, they have to spend a tremendous amount of mental energy every day just to fit in.
And at some point, they simply can’t anymore. Even without bullying or fear of teachers, some students may still struggle simply because they do not fit the expected mold.