> Paragraph 2 sets forth an exception to the general rule in paragraph 1 that employment income may be taxed in the Contracting State where the employment is exercised. Under paragraph 2, the Contracting State where the employment is exercised may not tax the income from the employment if three conditions are satisfied: (1) the individual is present in the other Contracting State for a period or periods not exceeding 183 days in any 12-month period that begins or ends during the relevant (i.e., the year in which the services are performed) calendar year; (2) the remuneration is paid by, or on behalf of, an employer who is not a resident of that other Contracting State; and (3) the remuneration is not borne by a permanent establishment that the employer has in that other Contracting State. In order for the remuneration to be exempt from tax in the source State, all three conditions must be satisfied. This exception is identical to that set forth in the U.S. and OECD Models.

https://www.irs.gov/pub/irs-trty/japante04.pdf

https://www.mof.go.jp/tax_policy/summary/international/tax_c...