Partly right, Shikinami is part of the Ayanami sub-class. Kancolle generally treats the Ayanami and Akatsuki sub-classes as their own separate sets. Shikinami up there is more closely related to Ushio and Akebono than she is to Fubuki. And both Fubuki and Shikinami are equally related to Akatsuki and Inazuma.
Still, sisters, half-sisters, or whatever they are to each other, it's nice to see these two together. They're still family in one way or another, so it's nice to see some bonding.
