in moon’s children, blueblood is cadence’s older brother! in the crystal empire the right to the throne is given to the youngest child, not the oldest. blueblood was fine with that, quite honestly- he hadn’t really wanted to be an emporer.
when sombra took over the empire, empress eleonora only had enough time and magic to spare one of her children- so she chose cadenza, the crown princess, heir to the crystal empire. blueblood, his family, and his people are still under sombra’s dictatorship.
blueblood isn’t arrogant, but he’s definitely traumatized and harbors some resentment towards his mother.