Japanese classes, originally written by Haruhiko Okumura and maintained by the Japanese TeX Development Community (https://texjp.org), including jsarticle, jsbook, and miscellaneous classes and style files.
The classes themselves do not automatically enable the support of Japanese language. You'll need to set up LaTeX environment appropriately so that it can handle Japanese.
In the above repository, we include the pre-generated cls/sty files to ensure proper encoding. The files have to be in ISO-2022-JP encoding to work properly on Windows. These files can be generated in a Japanese locale by running platex on the .ins files, for example
platex -kanji=jis jsclasses.ins
Haruhiko Okumura, Japanese TeX Development Community