I think you can add a machine that transfers souls, for example you can possess the body of another girl or two girls swap bodies and activities and scenes during the day or maybe fuse two girls to get a new special one.
even better that the fussions could make new girls that for example you had a group of Void Queens, you could fuse them to create a Void Empress (The empress is a fusion of Void Crystals and Bodies of the girls)
