If you are already inside the country, you can usually change your residence status at an Immigration Office without too much difficulty if you already have a company that is willing to sponsor you/
The keywords here, however, are “generally” and “usually” (especially in regards to Tourist Visas).
Some Japanese Embassy and Government websites say that, if you have entered Japan with a Tourist Visa, you MUST leave Japan first and THEN return to Japan with a Work Visa.
Other websites do not state this condition, and Immigration Officers usually follow internal guidelines and their own judgement on a case-by-case basis.
However, there are some important notes to consider:
1. It is illegal to come to Japan with a Tourist Visa for the express intent of looking for a job that will allow you to remain in Japan.
While this considered to be something of a gray area, if you are seeking to change your status from a Tourist Visa to a Work Visa, you MAY encounter complications at the Immigration Office – especially if they suspect that your intention was to enter Japan “via the back-door” to stay in the country.
2. It is absolutely illegal to work while in Japan on a Tourist Visa.
This is NOT a gray area. Some dubious companies may ask you to begin working for them while they process your immigration documents. Other questionable companies may even ask you to enter Japan on a Tourist Visa first and work for them on a “trial” basis before they will agree to sponsor a visa. Don’t risk it. The companies that expect you to work illegally like this are usually the ones with the worst labor law violations.
3. It is not illegal to work on a Working Holiday Visa (WHV).
However, the expectation is that you will leave the country after the Working Holiday Visa has expired.
Be that as it may, it is more reasonable for someone to have come to Japan on a WHV, find work, and then decided that they like the work enough to wish to remain and continue to do that work.
While there is always the potential that an Immigration Officer will frown upon the wish to change your status of residence, it usually carries less of a risk than trying to go from a Tourist Visa to a Work Visa.
4. The ultimate decision is up to the Immigration Office.
All the websites and all the company sponsorship in the world won’t help you if the Immigration Officer in charge of processing your documents decides that they do not trust your intentions, or they believe that the company that’s sponsoring you is a fraud.
C’est la vie.
5. Switching from “Instructor” status to “Specialist in Humanities” status because you changed jobs?
You do not have to leave the country at all to do that.
In conclusion, if your company says that you absolutely HAVE to leave the country to go to the Japanese Embassy in Korea or Thailand or anywhere that isn’t in Japan, call your local Immigration Office FIRST and ask them for advice.