The victims for me in this fantasy would be schoolgirls. Of course everyone would be over 18. The tormentors would be Nuns.

Nuns and schoolgirls would be dressed correctly in attire. Schoolgirls would have their uniform fastened correctly and buttoned up. The Nuns would subject the schoolgirls to aerobics-type-exercise until they start to become tired and strained. When the sweat begins to appear, the Nuns would loosen the tie on the schoolgirl and undo a few of the girl's buttons on her crisp white shirt and then punishment exercises would continue. For me personally, the school unform would stay on all the time, right to the very end. The Nun would grope the schoolgirl's body under the skirt and generally work and torment her. Eventually the schoolgirl will be exhausted and slick with sweat. She will then be made to do press-ups while attached to a dog collar leash, which the Nun is pulling upwards (not too hard) to force the press-ups a little.

Other costumes I would love to see:

Tennis Outfit as slave only.
Policewoman Outfit as slave and dominatrix.
Nun Outfit as dominatrix only.
Schoolgirl as slave and dominatrix.