To begin with, why phrase it like "You're not blood related"? In what universe is that a normal way to tell someone they're adopted?
In what universe is that a normal way to tell someone they're adopted?
In the universe called "Japan", a country where adoption isn't exactly easy, and blood ties are actually taken quite seriously.
I personally know of someone who was told that he wasn't the biological son this way (His real father died when he was a kid, then his mother got remarried), so saying "You're not blood related" isn't exactly out of hand.
The emphasis, again, on blood ties, is quite interesting aspect of Japan, hell, they have a fuckton of superstitions and shit around blood types, even getting to the point of discrimination (Search Bura Hara)