The fate of mankind is doomed in the early 21st century due to losing "purana," an essence of living force supporting all life forms. Not willing to witness the extinction of mankind, a vampire named Duo disclosed the secret of purana to humans, saving the latter from destruction. However, just like Prometheus in Greek mythology got punished for bringing fire to mankind, Duo is punished for breaking the taboo. The vampire sent to punish him is Zieg, Duo's best friend, or, more than the best friend.
Shinya Yukimura and Ayame Himuro are two scientists that want to find out if love can be solved by a scientific theory. These two scientists also have feelings for each other and want to be able to solve their feelings through similar theoretical facts. With this perfect opportunity, these scientists will attempt to solve the theory of the love they express for each other.