There is no system for adoptions in Japan. Why? It seems that few Japanese couples are interested in adopting a child. Why? For a start, the registration system makes it obvious to anyone who cares to look that a child has been adopted, and this, apparently, leads to a lot of "ijime".
More fundamentally, I think the Japanese put greater store in "bloodline" than people in the west.
But it is real shame that in a country that does not have enough children and which is filled to the brim with sad-looking couples pushing dogs around in little "dog carriages", that society cannot organise themselves to provide homes for all the children that it does have.