<p>Masada,</p>
<p>If you are a Japanese citizen and therefore don't need a student visa to spend a year in Japan, I wonder if you could simply go to stay with your friends and enroll in the local public high school? Either that, or a nearby private high school.</p>
<p>I think the best way to answer this question is for the family you would be staying with to contact the local ward office and the nearby high schools and see what they say.</p>
<p>good luck!</p>