Previously, Rachel and Zack found graves with their names on it but Zack ruined it despite of Rachel’s wish not to destroy her grave. How could someone wish so hard for their death?
It seems that there was someone who was making those graves — Edward “Eddie” Mason… and I have a feeling that Eddie and Zack didn’t like each other that much.
Looking at both Rachel and Zack on the intro reminds me of another anime — Soul Eater. Or maybe it’s just because of the scythe?