Couldn't Akatsuki call Fubuki Onee-san? The Akatsuki-class is a sub class of the Fubuki-class if I remeber correctly....
as far as i can tell, kancolle sees the three classes as different and most fanart does follow that. im not an expert on the destroyer classes but ive never felt a connection between members of the three classes to each other.
"Sub-classes" don't really work in Kancolle and both the fandom and Kadokawa treats it that way as far as how characters interact with each other. Especially with how sometimes, sister ships even within their own group end up being drawn by different artists. Murakumo is not usually seen as a "Sister" by the rest of the Fubuki classes particulary because she's drawn by Ayaki.
I think of myself as an elder sister.I want to try being spoiled.Whatever! Akatsuki is the number one Onee-san, you know!...but, from time-to-timePlease wait, Onee-sama!You're not very upbeat, Akatsuki-dono....Onee-chan.Harunaaa
Let's gooo!Therefore, it's fine if you feel like being pampered a bit.Akitsu Maru?