The heroine spent her childhood days in a lonely, remote place with her mother, Sumire, and her servant/subordinate, Luca. The Christmas she turned 16, she was invited to go and live together with her father, Mondo.
The dream she had ever since she was young was to live a happy life with her family together. Thus, with her long-yearned-for dream coming true, she took her first steps as a member of "Arcana Famiglia", a vigilante organization the frank Mondo is in control of.
The story takes place 3 months after that, on April 1st.