[ An old familiar face will come up beside D2, glancing down at the plaques laid out before him. William had recently spoken with Grell's newly appointed shinki, but upon seeing D2, he realizes how little he's interacted with her old one - the one he supposedly also worked alongside. ]

I would claim it to be another superstition created by mortals to ease their minds on complicated topics, but considering the gods are actually taking part in it, it must have more validity than that.