wait Ushio chan is younger than Akatsuki? Because she called her Onee san, and they're smaller than Ushio chan....care to explain please?

Ushio would actually be a couple years older but it's not like these comics usually take history into account.

in this story at least, Akatsuki and Sazanami position is as the onee-san, so even though Ushio is older than Akatsuki, they will call her onee-san. Heck even Oboro calling Ikazuchi okaa-san this doujin has some weird things happening at how they address people

lee15s said:

wait Ushio chan is younger than Akatsuki? Because she called her Onee san, and they're smaller than Ushio chan....care to explain please?

Ushio is actually Akatsuki's immediate older sister (Special Type DD #20 to Special Type DD #21). Ushio is, however, being considerate here, due to Akatsuki's reaction earlier. Note that both Akatsuki and "nee" are bolded here, indicating that Ushio is deliberately being careful with her word choice there.

Think of it as Hibiki's onee-san, with (Hibiki's) being implied. Adults will sometimes say it to (usually other people's) children as well 「お姉さんはえらいなぁ！」 "You're such a good older sister!"