Death
Relevant thread are under the flair Personal Finance » Inheritance Planning, also check Tax Inheritance / Estate.
For inheritance, please refer to the Inheritance Tax page.
End of life care
2022-04 How easy is it to have parents in law add me to their bank account ?
Will
The benefit of a will depends heavily on the laws of your country of citizenship, since those are the laws that will initially determine how your assets are distributed upon your death. Your country of citizenship will no doubt have rules that describe how to distribute the assets of someone who dies without a will. A will protects you against the consequences of those rules (or a future version of those rules, if they are changed in the future).
Will can be important for people in same sex relationship or other unions not recognized in Japan.
2023-01 What do I need a will for ?
DC pension inheritance
See this post.