Joe Tomei here. A friend of mine in Niigata has adopted two children and she’s currently setting up a group to help foreigners (and Japanese) exchange experiences or find out how to adopt/foster a child here in Japan. You can read about it here https://savvytokyo.com/fostering-japan-part-deciding-expand-family/
Unfortunately, it is much much harder to adopt/foster a child in Japan for a number of cultural reasons. However, it can be very rewarding. If you’d like to join the group, please contact me offlist and I will put you in touch with her. email me at tomeiter [at] gmail.