If you intend to engage in activities other than approved under your status of residence (category of visa) you need to apply to have your status changed at the regional immigration office. Along with the application and Alien Registration Card and passport you will need to submit documents of the intended activity to engage in. The documents you need top submit depends on the status of residence you are applying for. Application for Change of Status of Residence (English).
Alien Registration Card
If you are staying in Japan for more than 90 days you need to go through alien registration within this period of time. However if you are staying 90 days or less you do not need to register. Alien registration is done in the municipal office where you live. The municipal office will issue a Certificate of Alien Registration (Alien Registration Card) and you are required by law to always have it with you.
If you loose your Alien Card or if any of the registered facts changes, such as your address, you need to apply to have it changed within 14 days.
If you during your stay in Japan would like to leave the country, for example to travel or for a business trip, and still keep your Status of Residence. Application is made at the immigration office where you also will find the application form. To be issued a reentry permit you will need to have your Alien Registration Card or if you have not yet received it: proof of that you have applied for it. You can apply for a single or multiple reentry permit. A multiple reentry permit is a bit more expensive but allows you unlimited re-entrances to Japan during your period of stay.
If you do not have a valid reentry permit upon your departure from Japan you will need to fill out the Embarkation card for foreigner and also hand in your Certificate of Alien Registration (if you have one). In doing so any your status of residence in Japan stops which means that if you want to return to work or live in Japan you will need to apply for a new visa. If you have applied for a change of status or an extension of it the application and use Embarkation card for foreigner the application will be terminated.
If you do have a reentry permit you need to fill out the Embarkation card for reentrant when you leave Japan. Your status of residence continues and you will not need to apply for a new visa. It is very important that you make sure to use the Embarkation card for reentrant if you wish to continue your status of residence even if you have a valid reentry permit as you otherwise will loose your status of residence.
Where to find more information and help
The Ministry of Foreign affairs and The Immigration Bureau web sites are good places to start if you want to know more. You can also find a lot of information on the Visa forum. If you need more specific and individual help there are a number of lawyers that have specialized in visa matters. You can find many of the in advertisements in magazines targeting the foreign community.
Japanese Embassies and Consulates in your home country are still your best bet for the latest news and advance warning of any changes that may be happening, here is you one stop directory.
Embassy and Consulates around the world
A list of all addresses and telephone numbers to Embassy and Consulates in Japan:
Image courtesy of Staka / Wikimedia.