Japan’s immigration laws require you to have a bachelor’s degree (in any
subject) to be eligible for a work visa. Schools in Japan will prefer if you
hold a TEFL certificate. If you have a degree and your native language is
English everything is pretty much straightforward once you have found a
company to sponsor you. If you are recruited in your home country, your new
company will provide the paperwork so you can get a Certificate of
Eligibility (CEO). This can take up to 8 weeks to process. If you don't have
a degree the next option is to see if you are eligible for a working holiday
visa.