Ask to be homeschooled. Or ask to learn online.

Also you can skip high school and take university classes online or by mail. For example Athabasca university offers 16 year olds permission to take most classes world wide.

Other than a few classes most you don’t need a high school diploma to take them.

On the down side you would miss your prom and international classes cost more.

Covid19 might shut down some to much in person schools. So maybe online might be the only way to take classes for now.

Unless you speak and write Japanese fluently, you’re going to need remedial classes in everything. Maybe you’re a whiz at calculus, but it will be a steep learning curve if you need to translate properly so you can understand the lesson. Depending on where you’re living, you might also end up in a school for English speaking kids.

Do you understand the culture there? If you’re not quite familiar with how they think, you’ll also need to adjust, and that will take time and energy, which might make you grateful for the slower educational pace.

Hamamatsu has a huge Brazilian population, and a lot of people there have lived there their whole lives and don’t speak Japanese at all, Even the police speak Portuguese there!

Anyway, there are many moving parts to your puzzle (Where you’ll live, what schools will be available, etc.). Try to keep an open mind, and enjoy the journey!

I can’t add much to @snowberry‘s excellent advice except to say that you probably have a meeting with the headmaster of the school you are planning to attend and s/he will give you advice on what year you should be in. If your instruction will be in Japanese and you do not yet know the language, it may make sense to start studying it now if possible and also to possibly be in classes that you already have some knowledge of. Good luck with your excellent adventure and don’t worry too much about the bumps in the road.

PS Your English is very good assuming that is not your native language. You may want to enroll in a school where English is the language of instruction.

Repeat first year.
What do you have to lose?
It will be a great experience.

What does age have to do with it?

Since different cultures teach there way, it would be best to take High School in Japan at first level High School to make sure that you are on the same page as the class in learning.

And if you pick up the same information then you should advance quickly in Japan.
WInWin situation, right?

Do whatever they tell you to do. Japanese schools are very good and you will reap the rewards later.

I know from even just changing schools in the same country that everything is done different than what you’re used to doing. On top of that you’ll have to start over in making new friends. I’d think that it would simplify your process if you start in the first year with people your own age. That way you’ll be ahead of the game in your knowledge of the courses so your learning will be less stressful. That should assist you in having more social time in order to make new friends. You don’t have to tell any of your friends, whether old or new, that you’re starting over in year one. Just tell your old friends how much you’re enjoying your new experiences & there is NO need to tell your new friends that you’ve already taken first year. I doubt that anyone will ask.

I strongly suggest that you get this book: From Foreign to Familiar, by Sarah A Lanier.

It’s an easy read. It’s everything the reviews say and more. There are so many unspoken rules of Japanese culture, and you’re in for a rude awakening if you think you’ll fit in as well as you do in Latin America. Simply put, you don’t know what you don’t know. It could very well make the difference between a smooth transition and a rough one. https://www.amazon.com/Foreign-Familiar-Understanding-Climate-Cultures/dp/1581580223

Feel Free to PM me. My daughter has lived in Japan 8 years. I doubt she will ever return back to the states to live.. I’m certain she’d be happy to help you through any difficulties you have there.

I absolutely agree that you should not attempt to skip forward. I think it is highly fortunate for you that you actually have this opportunity. High school is when stuff happens. Lifetime friendships get reevaluated.
Kids group off and choose who they’re gonna hang with.
Romance takes shape and starts people into considering just who do they want to know better.
Second years already have their party lists figured out.
Where is a good place to hang after school? What places should be avoided?
I don’t think you will be ahead of these kids in curriculum, but even if you are, there is a lot to be learned socially.

My parents moved every couple of years from the time I hit fourth grade. High school is definitely the toughest of all.
@snowberry is a good resource for you here. You are fortunate she has offered her help.

High school can be badass, but you want to be prepared, or at least ready as you can be. Don’t believe you are ahead of things.
You don’t know what things you don’t know, until you need to know something that leaves you feeling clueless.

As an aside, I am excited for you. What an opportunity! Please stay in touch here. I think it will be fun for us to have you be a part of fluther, and include us in your journey.
By the way, PMs are private here. What you tell to one will not be told to anyone without your permission.