Even if a Japanese adopts you, you will not get the status of residence.
If you are (1) a real child of a foreign national marrying with a Japanese and (2) a minor unmarried, you can get the status of residence.
In Immigration Control and Refugee Recognition Act, the status of residence for adopted child will be limitedly given to the one who is under 6 years old.
Long-term (定住) visa based on Notification of the Justice Ministry will be given to Normal adoption.
Spouse or Child of Japanese National（日本人の配偶者等） will be given to Special Adoption.
Therefore, even if Children of six and above or adults are adopted by a Japanese, they can’t stay here for that reason in Immigration Control and Refugee Recognition Act.
If you do adoption without much thought, there comes the problem on dissolution of adoption after parents’ divorce.
Please be careful.
Solicitor & Immigration Lawyer Hitoshi Oishi