why wear pasties under a bra is there some kind of reason for that?
It is commonly used 'technique' to prevent chaffing your nips, usually by big-breasted woman or runners. The larger the chest means the pricier the bra (because not many stores carry products of that size), meaning you'd need to custom-order them. Some people orders them from a lower quality store so they would be cheaper, and those cheap bras often made from lower quality material-cloth, support, wires etc that makes your tits sway around inside them when you walk, and this can cause chaffing on your nipple. Using pasties can prevent that.
But in this case, it's just there as fancy censoring.