Tachibana Nobara, a cold and materialistic selfish woman, bought a little Siberian husky from a derelict-looking shop, replacing her late companion and also a pet-friend, a black Doberman pinscher. She named the new puppy Yuu. She found out that her little puppy wasn't really a dog after comparing his extraordinary thinking-skills and habits with a normal dog's cleverness. She agreed to take him as an assistant after he showed his human's form with a condition he must be a dog all the time except when she told him too.

In exchange of that, she needed to help him to break his curse as a little puppy which brought calamity to the one who admired him the most. Despite the deal, Nobara seemed to had no intention or initiative to even help Yuu to break his curse.

Regardless of being cursed, Yuu also had a superpower for which he could induce electricity and even lightning bolt without the use of magic either in the form of a human or a dog. As one of the chosen hero, the great 7 sentinels, Nobara's only job was to slay vampire or apprehend them if necessary. Her current mission was on investigation of the vampire's third method of conquering humanity after they had achieved twice failures.