[sarasi]

Sangetsu, I was under the impression that teachers in public schools in Japan are koumuin (public servants), and koumuin must be Japanese citizens. People teaching as ALTs in public schools usually work 29.5 hours- just below full-time. You know non-Japanese people employed fulltime as regular teachers in public schools?

As for becoming the principal, obviously someone has to be an ordinary teacher and work their way up to reach that point, and that can take 20 years or more. Are you sure you will like Japan enough to want to stay that long?