User blog comment:HazelQuill7445/Awesome fan art/@comment-24573226-20160620182448/@comment-4010415-20160620200821

Strapless bras exist, yes, but an awful lot of the dresses worn to the dance had a very open back or a mesh back, and there was absolutely zero sign of a bra of any sort in sight, so I can only assume that the dresses had built-in bras.