This tag is to be used when the protagonist is known to be an adopted child from the beginning of the story. Or else, the part that he/she is adopted should play a big role in the plot. It is recommended not to use this tag, if the fact that the protagonist is an adopted child is discovered in the later part of the series, as it will become a major spoiler.
I fell in love. Her name was Shirasaki Yukino. I could only look at her from a distance. However one day I heard that she already had a boyfriend. Even if I love her, I can’t have her. The devil sent me an invitation. I can make her mine!