Didn't Natsuko and Haruka decide earlier they weren't going to swap with other people?
Tehcnically Fuyumi is the only swapper who has explicitly refused to try swapping with anyone else. Satsuki is currently a non-swapper who identifies strongly with her body, and thus refuses to try. Natsuko has come close to possibly doing it with other people a couple of times, but she's always found a reason to back out of it before trying. Haruko has seemed somewhat eager to sample other peoples' bodies in the past (specifically Yume's), but has been seen to be looking on with an unreadable expression when the idea of NATSUKO swapping with anyone other than her has come up. Akiho doesn't seem to have any inhibitions against trying to swap with anyone else, although she eventually concluded that there would be "something wrong" if she (in Fuyumi's body) were to swap with Natsuko at the amusement park. And lastly Yume seems all in for the idea and has been trying to get a kiss with any of the swappers any chance she can get, to no avail thus far.