Basara Tōjō met his two cute little sisters, Mio Naruse and Maria Naruse. The two sisters revealed themselves as a member of the demon clan and Basara as a member of hero clan, demon clan's enemy, and is not related by family. Mio is the future Demon Lord and since Mio's power is not fully awakened, Basara will protect her from the demons who are after the power she inherited from her deceased father, Demon Lord Wilbert.

 

While Basara, Mio, and Yuki have picked up their seemingly ordinary lives, they were attacked by magic-wielding humans when preparing for the upcoming sports event. Basara tries to become stronger by strengthening the testament when Rukia, Maria's sister, suddenly appears. Unknowingly, the war deciding the future of the demon realm has started.