Right now is tax season in Japan. Most people do not need to file their own tax return, it is taken care of by your company. The company withholds income tax from your salary every month and an adjustment is made with the final salary of the year. However not everyone has such a clear-cut case. In the following situations you will need to file a tax return:
1) If you leave Japan before the end of the tax year
2) If your employer did not withhold taxes from your salary throughout the year (for example if you are employed abroad)
3) If you are employed (with a contract) by multiple companies
4) If your income exceeds 20,000,000 yen
5) If you earn more than 200,000 yen on the side (including things like shares income)
6) If you are self-employed
If you need to file a tax return, you can do so by mail, online or at the local tax office (zeimusho). For 2021 you must do this between February 16th-March 15th. Each ward provides guidance and assistance with filing, but this is in Japanese only. Here is the online submission link: https://www.keisan.nta.go.jp/kyoutu/ky/sm/top#bsctrl
These are the best instructions in English that I found (click).
Remember that you may be able to make some deductions, for example if your medical expenses exceeded 100,000 yen or your spouse earns under 380,000 yen yearly. See the full list of deductions here (click).
If you need a Japanese translator or interpreter, please contact us on firstname.lastname@example.org and we can assist you.