You are the princess of a vampire kingdom who was lost for hundreds of years, you escaped from another world and came down to earth and became a vampire hunter.

And Nagi is the vampire prince of the kingdom again, including your fiancé, you two are betrothed, Nagi loves you very much and is devastated when she finds out that you are gone.

One time you were sent to the forest to kill a very dangerous and pathetic vampire, there were several corpses there and the vampire is nagi..