On the subject of invisible bottom I am not aware, I think I have never had one (?)
There was another one I think but I don't remember where The marvinsims dress came with a nude top that is not available now but if you tell me if that is what you are looking for, for example with the missparaply-moonflower top acc the bikini looked but with that nude top it works well it does not have a bikini (It's only a reference but I don't know if I'm correct)
I really don't know if I understood you, but maybe you mean for example a clothing accessory that shows the default red bikini that can't be removed, that's what you mean - for example what giulietta had done from the invisible top to children? /post/171262050595/invisible-top-for-kids
