Not sure about these days but traditionally a visa is used to enter a country therefore it wasn't possible to get a visa when you're already in-country. I went to Japan as a tourist before my working visa was ready but had to fly to Hong Kong to get it. But this was decades ago. Things may have changed.
If you enter Japan on a tourist visa and take up employment, you will still need to leave the country and start applying abroad. You cannot change a tourist visa to a long-term or working visa. However, once you have a long-term visa, it is possible to change or alter its status.
Changing visa status due to job change, marriage, divorce or starting your own business. Visa & Immigration Procedure in Japan. Visa categories and requirements in Japan including work, spouse, business manager and highly skilled visa.