Public schools vs. international schools in Japan?

This is a difficult comparison, and it's especially challenging to generalise and say one is better or worse than the other. Each expat family has a different situation and different priorities. That said, I've worked in a Japanese public school and these are my observations...

Japanese public schools demand a commitment from student's from very early in the morning until late at night. If children are not commuting to/from school, attending classes, engaging in the REQUIRED extra-curricular activities and then studying to complete the appropriate assignments, then they're probably sleeping. Especially at the high school level, where the all-important entrance exams are looming in the background, Japanese public school is super stressful.

So much so, that in my personal opinion, I would send my child to a public elementary school, maybe a public junior school, but not a high school.

There are plenty of international and private schools around that look to acheive a better balance between school and life.