A group of close friends try out a 'men's swimsuit challenge' they found on the internet! They wear swimsuits borrowed from boys in their junior classes and test their courage at the prefectural swimming pool! They expose their flat, round breasts in a public place! They might have been seen... (sweats). They greet the users, swim backstroke, and complete embarrassing missions that make it even more extreme! And then they end up being found out to be girls...!?