The Witch Boy #1

Males in Aster's extended family are shapeshifters, while females work magic. Aster, who is fascinated by magic, attempts to learn on the sly. When an unknown being kidnaps his male cousins, he enlists the help of a non-magical girl and attacks the monster, completing a magic circle to trap the monster within. Grandmother reveals that the monster is her brother, who spurned the family on being denied the chance to study magic. She rules that Aster may break tradition, and study as he chooses.