Certain visas of certain countries fall under a non-immigrant visa. In these countries, a short-term visitor’s visa is most likely to fall under a non-immigrant visa. If a visa-holder of these countries looks for a job while they are in these countries, that might be inconsistent with a non-immigrant intent, and they might be deported in the worst case.
There is no non-immigrant visa in Japan. Interestingly, short-term visitors are allowed to look for a job and even rent an apartment if they want to stay in Japan for a few months to look for a job. Even so, they are not allowed to actually work unless they change their status after finding a job. Plus, they cannot change their status in Japan in this case.