Flat-chested girls found at a hot spring inn take on the "flat-chest challenge" by entering the men's bath with only a towel, aiming for a huge cash prize!! They boldly pretend to be men, leaving their flat breasts completely exposed as they charge into the men's bath!! If they can clear various missions without being caught, they win the prize! Naturally, the more erotic and difficult the mission, the higher the reward!! Will they get away with talking to male guests!? Secret handjobs without the other men noticing! Secret blowjobs!? They even attempt the highest difficulty "flat-chest sex," but... do they get caught!? The flat-chested girls get just as excited as the aroused male guests! Will they go all out and join in a friendly, erotic orgy to successfully "collect a massive amount of cum" and win the big prize!?
