It's hard to answer a question so broad and having no idea about your background. Have you graduated from university? Are you in university? If you have graduated what work do you do right now? Do you want to live and work in Japan for your life? Or is this "yeah I just want to experience it for a little bit"?
I don't need anything super specific but it would be good if we could know "oh I'm in my 1st year of university in engineering (or Japanese literature or pre-med)" we could suggest "then look for an exchange to a university in Japan for your 2nd or 3rd year if possible".
English teacher is probably the easiest and realistic for most people but it's not a job you would want for your career.
If your goal is longterm work in Japan:
I don't want to say give up that dream but I think you should ask yourself some tough questions about why you want to work in Japan. If it's at all financially possible - I would look at a vacation there first where you give the place an honest look and decide "do I want to stake my entire future on this place even if it's likely I will not succeed". The deck of cards will be stacked against you trying to work in Japan. It will be against you succeeding in Japan if you somehow get a job there.
Personally I can't see myself ever risking that much on any country let alone a place like Japan.
Some options that could potentially get you work in Japan but still provide you with a "safe" career: researcher/professor at a university, diplomat, public accounting, finance and many other professional white collar jobs (at large multinational firms with offices in Japan of course).
I understand I'm being negative and pessimistic in the eyes of some people but I think I'm being a realist. The vast majority of people who live in foreign countries do return home. There is very little opportunity to advance in the foreign country where you are not a native speaker and frankly - you miss home.
I would say the same thing to anyone who said "I really want to work in Italy" or "I really want to work in Spain" or South Korea or anywhere else. Language barriers are a big deal and they will stop you from advancing in your career. You will feel isolated and lonely at times.
Now some people do stay. The return rate is not 100%. But it would be better if you could figure out beforehand just how committed you are.