Twelve-year-old Touta Konoe has spent his whole life in a rural town. He dreams of one day going to the capital, where there is a tower that reaches into space. To fulfill his dream, he has been tasked to defeat his teacher and caretaker, Yukihime, who will then permit him to go to the capital.
Touta's life turns upside down when a bounty hunter arrives to claim a prize on Yukihime's head. In a desperate attempt to save both his mentor and friends, Touta follows Yukihime's instruction to drink her blood, turning him into an immortal monster capable of defeating the bounty hunter.
Yukihime reveals herself to be Evangeline Athanasia Katherine McDowell, a centuries-old vampire. With her identity now exposed, she and Touta flee to the capital and embark on an exciting adventure that will change both of their lives forever.