In the Vampire Mercenary Specialized School, "1000 Years Academy," the most unvampire-like vampire at the academy, Aru, and the human transfer student, Kei, meet by chance. But what they didn't know was that it was a fate the world depended on.

Deep in the heart of 19th Century London, a young nobleman named Cain walks the shadowy cobblestone streets of the aristocratic society in which he was born. Forced to become a Count upon the untimely death of his father, Cain assumes the role of head of the Hargreaves, a noble family with a dark past. With Riff, his faithful manservant, and Mary Weather, his 10-year-old half sister, Cain investigates the mysterious crimes that seem to follow him wherever he goes.

The world is said to exist with yang, the world of humans and yin, the world of mythical beasts in conflict with each other. A long time ago, two clans who were involved in an unending war exchanged an inviolable pledge and started living in their own worlds. At that time, the king who ruled over all the mythical beasts gave his own sword to the human queen whom he dearly loved and vowed that if the queen or her descendants ever fall into danger, he himself and his descendants will surely come to save them...And now, when the third war is about to begin, a beautiful swordsman with the blood of the king of beasts had a fateful encounter with the aloof king of mythical beasts, and the story begins!

This is a story about 2 childhood friends, Masato and Yuki, that reunite as teenagers.
Masato is surprised to find that Yuki has become so cute, but even more surprised to realize that Yuki was, and still is, a guy.
Yuki's affection for cross-dressing leaves Masato with feelings of discomfort and fright.

In the big city, drug crimes run rampant. Eto Kai and Kurabayashi Hal are two newcomer investigators who fight against them. In order to save people from modern society, poisoned with drugs, the two turn to face an invisible enemy...