The period of stay is determined together with the status of residence when the foreign national lands in Japan or changes his/her status of residence, and the foreign national may only reside in Japan for this stipulated period of stay.
Consequently, a foreign national wishing to continue the same activities in Japan with his/her present status of residence beyond this stipulated period of stay must apply for permission to extend the period of stay no later than the last day of that period of stay. Extensions will not be permitted if the purpose of the stay has already been completed or there are other problems connected with the status of residence.
Applications for extension of period of stay are basically accepted from three months before the expiration of the period of stay if the period of stay is six months or more.
If a foreign national who has applied for permission for an extension of period of stay does not receive the results before the expiration date of the period of stay, he or she may continue to stay in Japan with the status of residence then in force for two months from the expiration date of the period of stay or until the decision of the results, whichever comes earlier. If two months have elapsed since the expiration date of the period of stay without any measures being taken, the foreign national will be unable to stay in Japan.
If the status of residence is a temporary visitor status, extensions will, in principle, be granted only when there is a truly excusable circumstance from the standpoint of humanity or a comparable special circumstance. However, under the visa exemption agreement, nationals from Ireland, Austria, Switzerland, Germany, Liechtenstein, the United Kingdom, and Mexico may stay for more than 90 days and stay up to 6 months if permitted by the procedures for extension of period of stay at the Regional Immigration Bureau before the expiration of the period of stay.
Regarding period of stay, please refer to the following web site,
A foreigner residing in Japan who wishes to cease the activities in which he/she is currently engaged and to engage exclusively in activities belonging to a status of residence other than that which he/she presently holds must apply and receive permission for a change of status of residence. For example, a foreign national dispatched from a parent company in a foreign country to a subsidiary in Japan and currently residing in Japan on an "Intra-company Transferee" status of residence who wishes to resign from the company to which he is dispatched and to invest in and operate his own company needs to apply and receive permission for a change to "Business Manager" status of residence.
However, applications for a change in status of residence are not automatically approved, and permission will not be granted if the new activities do not correspond to the requirements and criteria of the status of residence sought. A foreign national residing in Japan on a temporary visitor status will not be permitted to change his/her status of residence unless the application is made based on special and unavoidable circumstance.
If a foreign national who has applied for permission to change his or her status of residence does not receive the results by the expiration date of his or her period of stay, he or she may continue to stay in Japan with the status then in force for two months from the expiration date of the period of stay or until the decision of the results, whichever comes earlier. If two months have elapsed since the expiration date of the period of stay without any measures being taken, the foreign national will be unable to stay in Japan.
Please refer to the following website for procedures for changing the status of residence.