Although the qualifications of specialized schools are not recognized in China, it is still a formal education in Japan, which is different from training schools. Visa is also a study visa.
If you want to pursue further studies, you can apply for university courses. Is your current education a four-year undergraduate course? If yes, there are many colleges of large art universities that can apply.
For example, the composition research room of Osaka Conservatory of Music.
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Tokyo Conservatory of Music majored in composition and command.
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It is true that special schools basically teach from the basics, which may not be suitable for your situation. But you can look at the website and think about whether the research topic of the university is what you want to learn.
Art colleges have no rigid requirements for language. They don't have to have a certificate of 1, and they don't have to have test scores, but they must be able to communicate and attend classes smoothly, so they basically have to reach the level of 1, but there is no hard and fast requirement for certificates. College entrance requires Japanese level 2 or above.
If you don't have basic knowledge of Japanese, you'd better go to a language school to learn Japanese first to adapt to the living and learning environment in Japan. Whether you are suitable for attending a special school or a junior college depends on your own consideration, so it is better to go to a language school first and then find out for yourself on the campus open days of universities and special schools.