Nana & Kaoru: Black Label, Volume 1 Paperback by Ryuta Amazume

Meet Nana and her grumpy, virgin childhood friend Kaoru. These two share a secret that they couldn't possible reveal to anyone else: their special breathers they use to unwind. During a summer vacation, Nana decides to take a break and takes off with a certain someone to the countryside. The fresh air, the towering mountians, the soothing sunlight, rice fields as far as the eye can see... All so she can have her usual breather before exams. But is this what breathers were always like? To Nana, these new ones cannot compare. Perhaps by chance, or even fate, she is ushered into a whole new world in the countryside.