Small-breasted girls gather at the mysterious hot spring "Big Breast Hot Spring," which has the effects of breast enhancement and pink nipples that women envy! In the large bath, everyone gets a massage lesson! First, by themselves! Then the person next to them! Line up and start from behind! Finally, everyone gets a massage in a circle! A wonderful lecture using the hot spring increases the girls' sensitivity, and in the second half, they get individual lectures in the private open-air baths! However, it's actually a man who is doing this! The girls are embarrassed just to be seen naked, but... as all the breast augmentation points, such as their breasts, nipples, and necks, are stimulated... they gradually begin to feel it, and unable to contain their excitement, their hands go to the penis...