Sometimes you need to do something bad to stop you from doing something worse.
The vampire is a resonant metaphor - a way to frame the deeper intentions of the story. This is a love story, but also the story of two exceptional outsiders who, given their unusual circumstances, have a vast overview of human and natural history, including stunning achievements and tragic and brutal failures. Adam and Eve are themselves metaphors for the present state of human life - they are fragile and endangered, susceptible to natural forces, and to the shortsighted behavior of those in power.
Spirited Away (2001)
“Once you’ve met someone, you never really forget them.”
Now in these last agonizing minutes of life you have left, let me answer the question you asked earlier more thoroughly.