not like they would be seeing something they already had not. no neck stub to tie the strap around around? Some artists draw a neck in her collar. Other leave it up to the imagination.
Sekibaki is using her heads eye level to look right at Tojiko's ass. Seki even has a blush while looking at her ass, I think that's why the other girls are sorta covering up. Her intentions for the girls bath are quite clear.