I admit I'm definitely not an expert on women's clothes, but the thing Kuroshio was holding looks more like what was described to me as "a shelf" than a bra. Basically a piece of cloth used when the support of a cup isn't needed mostly to keep your nipples from visibly poking up through your top.
Considering Nui here doesn't need much support, as long as her top isn't made out of something really scratchy, I could understand not noticing.
I admit I'm definitely not an expert on women's clothes, but the thing Kuroshio was holding looks more like what was described to me as "a shelf" than a bra. Basically a piece of cloth used when the support of a cup isn't needed mostly to keep your nipples from visibly poking up through your top.
Considering Nui here doesn't need much support, as long as her top isn't made out of something really scratchy, I could understand not noticing.