People fall in love in the most mysterious of ways. This statement seems to be especially true for the affluent genius playboy Ryou Amakusa. When he nearly falls off the stairs one rainy morning, a girl named Ichika Arima saves him. As if by fate, Ryou encounters Ichika again later that night; she happens to be the best friend of his little sister, Rio. Wanting to "thank" her, Ryou attempts to woo Ichika by employing his usual flirtatious tactics only to be immediately shot down, his target creeped out by his behavior. Rather than being discouraged, Ryou instead becomes more enthralled by her, and he begins to do everything he can to steal Ichika's heart despite receiving disgusted reactions each time. However, as time passes by, will Ichika remain repulsed by Ryou's creepy yet dedicated advances?

Following the events of their trip to Okinawa, Saitama University graduate students Shinya Yukimura and Ayame Himuro have failed to obtain the data necessary to scientifically prove their love for each other. Unable to replicate the exact conditions of the trip, the two stubborn scientists decide to seek help from elsewhere in the university—the Biological Sciences department. Assisted by fellow graduate students and longtime couple Chris Floret and Suiu Fujiwara, Yukimura and Himuro begin to quantify their feelings by measuring their output of oxytocin in various romantic situations. The two scientists soon find that their feelings for each other are nothing compared to that of a mature couple. It is here that Chris poses a question to both Yukimura and Himuro: what will they do if their "affection" is proven not to be love after all? Desperate to find a scientific rationale for the discrepancy, Yukimura puts everything on the line to prove that their "love" is real.