The story of Otak川 Little Devil takes place in Kyoto in May, with the gurgling of the Otak川 River. After repeating a grade, Abe finally passed the entrance exam for Kyoto University. He became good friends with Takamura, who was fascinated by Japanese culture after living overseas. One day, while returning from their part-time jobs, the two encountered Sugihara, an upperclassman from the same university. Sugihara invited them to attend the welcoming event of the Kyoto University Seiryu Club. The Seiryu Club was a strange club with unclear purposes. Abe fell in love at first sight with one of the club members, Kyoko Sarayashiki. In order to get closer to his crush, he applied to join the club without hesitation, and Takamura also became a member. Besides Abe, Takamura, and Sarayashiki, the new members of the Seiryu Club included Nanami Kumiko with her glasses, Arima Manabu who had an air of superiority, and the identical twin brothers trio, Miyoshi, all of whom were eccentric individuals. On the night of the Gion Festival, led by Sugihara, the members of the Seiryu Club, dressed in blue yukatas, gathered at the intersection of Shijo and Karasuma streets. Then, groups wearing white, red, and black clothing arrived subsequently; they were from Ritsumeikan University, Ryuukoku University, and Kyoto Sangyo University respectively. After introducing themselves, the four groups dispersed. Confused, Abe later learned that the Seiryu Club was the inheritor of Kyoto's thousand-year-old secret ritual, Horomo. They had to manipulate a spirit called "little devil" to engage in opposition with the three teams representing White Tiger, Vermilion Bird, and Black Tortoise. There were ten people in the Seiryu Club, and each person had to control a hundred little devils. Following the upperclassmen, Abe and others began special training. They studied ghost language and practiced bizarre commanding gestures. However, even after half a year of continuous training, they hadn't seen a single little devil. One evening, the Seiryu Club arrived at the Yoshida Shrine. In a solemn atmosphere, Sugihara suddenly started singing strange songs and dancing naked. Gradually, the new members like Abe also got caught up in the frenzy and danced wildly. It turned out that this was the sacred Yoshida Succession Ceremony. After the ceremony, Abe and others officially became the next generation of Horomo Masters. Instantly, a thousand little devils appeared before them. The battle of the Four Symbols was about to begin. As the Seiryu Club busied itself with intensive training, Abe suddenly learned that Sarayashiki had already started dating Arima. Deeply affected, Abe proposed to leave the Seiryu Club. Sugihara indicated that an internal battle following the ancient rules of the seventeen clauses must be conducted. With the support of Takamura, Nanami, and the Miyoshi brothers, Abe formed a team. The remaining five people constituted the powerful Arima Team. However, they did not know that there was a terrible secret hidden behind the seventeen clauses.