I remember reading a manga a few years ago about that features a boy who dresses as a girl and his twin sister.
The backstory of the two was that the boy did not go to school and dressed as a girl at home to impostor his twin sister to escape their father's abuse, as he does not usually abuse his sister or abuse him when she is around. One time however, the father ends up abusing the twin sister (he was drunk or something), kissing her hair, saying it reminds him of their mother. Later the twin sister goes to their actual mother (who is divorced with him) for help but the mother brushes her daughter off, telling her to solve her own problems. So when it happens again (or something like that), she shaves her head completely.
Since then, even after her hair grew out, the twin sister does not let anyone touch her hair - not even her brother - with the exception of her female best friend (that if I remember correctly she has some romantic feelings for?).
Another detail I recall is that the father was a photographer and obsessed over taking pictures of a bird he has, but at some point the bird dies but I don't remember why.
The story is set after all of these have taken place, and is told in the perspective of another boy who goes to the same school as the two of them.