Based on the Immigration Control and Refugee Recognition Act, your status of residence may be revoked if you do not participate in activity as a student continually for over 3 months. (However, this does not apply in cases where you have a valid reason.) Taking a leave of absence falls within this category, so please consult with your academic adviser and academic staff in charge of international students before doing so. Furthermore, activities such as part time work will not be permitted during the leave of absence.
If you graduate or withdraw from UTokyo, you will be required to leave the country even if your “Student” status of residence is still valid. If you intend to remain in Japan for purposes other than study, please change your status of residence to an appropriate category as soon as possible. You are not allowed to continue to stay in Japan with "Student" visa status.
cf.) Checklist of necessary procedures before leaving Japan