When you graduate from the university or your employment contract finishes and you leave Japan, you will need to take various procedures. On the following page, the necessary procedures are listed. Please prepare well in advance.
https://www.u-tokyo.ac.jp/adm/inbound/en/life-daily-leaving.html
UTokyo alumni organize alumni associations in Japan and around the world. Please take advantage of this network of alumni who are active around the world.