Asuka's Links
She is Kiryu's big sis. Since most of their sisters are years older than them, the two of them would become the older siblings for their 2 younger brothers. She dotes on all of them, but treats Kiryu more of an equal. She's willing to throw hands with anyone who bullies her brother
Angela is Kiryu's older sister, who inspired him to pursue being an idol himself. The two of them only have a 1 year difference, hence they are very close.