Original heroine, Harry's twin sister
What if there was a delicate-looking girl with black hair and blue eyes in Hogwarts?
What if the savior's sister was a Slytherin...
Garros: Wait, I have a younger brother? Potter?
(If you can't write a copy, just leave it at that.)
Ps: The protagonist is adopted and lives in the Muggle world. He knows that he is not the biological child of his adoptive parents, but he does not know his own life experience. The third-year protagonist only recognizes Harry, and he doesn't even know it at first.
Intention: Know your mistakes and correct them