Decent pads do bounce. Especially bigger ones. The best ones are made from the same stuff that medical breast implants are made of. These kind stick to you (with adhesive) and will bounce hard enough to be painful if you aren't wearing a bra of some sort. I would imagine that if Sakuya does wear them, she would have only the best.
They also pick up heat from your body after wearing them for little while, so they're warm to the touch. And they do have nipples as well. (I once had a girl poke my chest with her finger in an attempt to determine if they were real or not, and she concluded that they were real. She nearly jumped out of her skin when I said they were fake...)
