[makeitdouble]

That's implied. If you're working with your tourist visa you're changing the purpose of your stay and thus lying regarding your visa declaration:

> Single-entry short-term stay visa for the purpose of Tourism (for a period of up to 90 days) (Note).

> [...]

> If you wish to visit Japan for other purposes or for a long-term stay, please submit your application to the Japanese Embassy, Consulate General or Consular office with jurisdiction over your place of residence.

https://www.mofa.go.jp/j_info/visit/visa/visaonline.html

[nerdbert]

The purpose of the visit is still tourism, even when people are also working remotely. Otherwise they could have stayed home and worked remotely.

[makeitdouble]

Setting aside my other response, a better way to look at it is that you declare your purpose on entry, but you're not the one judging if it's appropriate or not.

We/You can see remote work as not invalidating your claim, but that's just how we feel, not how it will be judged. To your larger point, the rules being mildly fuzzy aren't helping foreigners in general, it's usually more leeway for the authorities to pick and choose.

[makeitdouble]

That's like saying your purpose is enjoying the scenery, because even if you're shooting a new photo book, you put your pleasure above all and taking professional photos while looking at the landscape is just a small detail.

I mean, we can invent a lot of way to present it, it all comes down to how the immigration office interprets it (as far as I know, the only real test is suing them when they ask for the money)