I remember that Musashi never call Yamato is nee-san or something similiar.
Yep. She addresses Yamato as just "Yamato".
Hurry!!...yes... Yamato is... all righ-Neesan! Another ramuneeee!!fufu... the sky's beaut...It's nice weather today, it's very hot... Really fucking hot... And so, today as well, I'm bringing everyone some cold ramune... that's my job...Really, this god-damned girl...This sunbrella is also given to me by Admiral, but it's wasn't in consideration for my body... Everything is for the ramune... warm ramune just isn't tasty...