He was eternally a social boy, and Kid hated him for it.
The first time Death the Kid and Black Star met had been before either could talk, much less walk; growing up sharing babysitters and cribs and playpens and diapers, you'd think they would have grown close, but the opposite couldn't have been more true. The two were polar opposites and clashed at almost every possible interval.
Blue hair, green eyes, ever-present grin, even more present friends. Below average grades, more often than not in detention, and yet he charmed teachers and students alike with nothing more than a ridiculous remark about surpassing the gods.
Growing up so closely entwined had introduced them to the same people, but that didn't make them all friends; Kid preferred the company of select few, but Black Star let anyone and everyone near him to experience his "greatness". Kid found himself with only two close companions; sisters, devils, angels, depending on who you asked. Even they were friends with Black Star by association with a girl close to him who was Liz's age. It seemed that no matter who he met, they all thought well of Black Star. It was infuriating.
He was eternally a social boy, and Kid envied him for it.