From a US point of view maybe but it’s complicated in Japan. For starters you are not allowed to work remotely on a tourist visa waiver and work done remotely I Japan is not “foreign sourced income”, at least not for a normal situation. There’s conditions which may trigger tax residency, and finally regardless of your status, work done in Japan can cause liabilities for the US company.

Also the posts I mentioned are almost universally “I assume or have assumed that I can just buy a house and work remotely from Japan”, but there a few that are looking for loopholes to be a digital nomad.