You need to have Graduation Certificate from Junior High shool in Japan or in your country.

Senior High schools (koukou)(3 years)

You can't choose what your child will learn in grades 1 to 9. But you can select in koukou.

The pattern of koukou;

full time

part-time

night-time

Specialized Training schools (senmon-gakkou)(3 years)

you must check schools carefully that won't give your child "certification of grade 12" because there're many schools that make you confused anywhere.

Colleges of Technology (Kosen) (5 years)

The majority of them are run by the national tax. They focus on technologies.

Each student receives an academic degree. Also, many Faculties of Engineering at the best universities in Japan accept the graduates in the university's 3rd year or master course.

https://www.kosen-k.go.jp/english/what/educationsystem/educationsystem/