Responses
This is an instance of yes but no.
If they're not brother's in paper nor by blood then people should stop calling this incest. They're now like childhood best friends.
I know right
I understand why people see their relationship as incest but it's just not
They were raised as brothers .. but they aren't brothers, even in a legal sense I guess. If Yu's mom was able to call him back I doubt she ever gave up her parental rights and his birth certificate should have his biological father listed. Then A's mom and dad would've just been his guardians, and it is stated that he's a foster child, a totally different from a adopted child. Yu knows this from when he was a child. Legally speaking, there's nothing wrong since the both of them might not even be in the same household registration.