Immortal lead characters, purple branding and ex-boyfriend drama? Yet somehow, one of New York City’s newest vampire love stories bears the most resemblance to a show about a boy working on a song. Blood/Love is full of surprises for all your senses, starting well before the first notes. From the moment you enter the lobby of Theatre 555, an intimate off-Broadway venue on 42nd Street near 11th, you’re transported to…