[Sangetsu]

There is no tuition required to attend a Japanese public school, but you'll need to enroll under some type of foreign visitor program as regular students must pass an entrance exam to attend high school.

As a dependent of a Japanese resident, or as a student, you should be able to get a one year visa, you can inquire at the Japanese Ministry of Foreign Affairs (MOFA for short) for exact details. It would be best to spend a little time here before making any plans for a longer stay.