beta
It's not a yaoi. It has a female protagonist which was adopted and was in love with her brother. She goes to this new school filled with children who have powers called 'bullets' I believe. Then goes on to become a bodyguard of the black haired dangerous guy in school. The art style is pretty unique: thin lines and angular faces similar to 'Karneval'. Thank you!
There's this thing where a male has too many female chromosomes and develop bewbs. So basically XXY.
And sometimes even XXXY. That's why some males have more bewbs than others.