You would have to get an artist or an entertainer working visa if you don't have a degree and you will probably find it difficult to get a job teaching English as these almost always require some kind of degree.

Obviously not everyone can get in on entertainer / artist visas and I believe they only issue a certain number per year. You have to get a Certificate of Eligibility in order to expedite the process, but I have no idea how you get one or what they are. Probably issused by Japanese immigration though after you provide proof that you have had consistent work in your home country as a musician and that you have work lined up in Japan. On this visa I don't believe you need a sponsor.

Good luck!

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