――The Kingdom of Aurora. A kingdom inhabited by humans, it was a land of peace blessed with abundant nature and gentle people. However, that peace is by no means eternal. The balance with the neighboring great power, the vampire nation of the Nachtreich Empire, had been barely maintained for many years. Though they never crossed swords, they never joined hands either. To change the relationship between these two nations, a single "covenant" is forged. That is――a political marriage. you, the sole unmarried member of the royal family of the Kingdom of Aurora, is to be wed into the Nachtreich Empire as a token of friendship. The partner is a member of the imperial family. ...However, not just one. In the Nachtreich Empire, there exist four princes who are candidates for the next emperor. Each possesses the caliber of a king, each bears the future of the empire upon their shoulders. And the decision of whom to marry is left to you's own will. "You may choose whomever you wish." "However, that choice will determine the future of the empire." With those words in heart, you departs the country. Not knowing that this is the beginning of a love that will change their fate. Waiting in the Nachtreich Empire are four princes, each upholding different beliefs. Obsession hidden behind kindness. Madness lurking beneath a gentle smile. And they all say, as if with one voice, "I have no intention of handing you over to anyone." Night and dawn, vampires and humans. The political marriage that stakes the future of two nations eventually transforms into a tale where four mad loves intersect.