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 Chiba University, you will be required to leave the country even if there is still time on your status as a "Student" unless you must immediately change your status to an appropriate status of residency. Continuing to stay as a "Student" will be illegal.