The Water Navy Xuanwu has become Impermanence.
Upon hearing this news, although I hadn't predicted it beforehand, I wasn't surprised. The Water Navy Xuanwu, like me in the past, was a candidate for Impermanence, recognized by the world as someone with the potential to become Impermanence. In the Post-mortem World, I have even fought with the Great Demon Xuanwu, so I, more or less, have witnessed the kind of power Water Navy Xuanwu could possess once reaching this realm. Seeing them still at the Great Success Rank afterwards would probably be rather anticlimactic.
The other Great Demons all have their prototypes as Impermanence, but both the Catastrophe Demon and the Great Demon Xuanwu, at the time when they were summoned by the Naraku Gospel, were still not Impermanence. This isn't meant to diminish the value of Impermanence, but if Water Navy Xuanwu couldn't even manage to become Impermanence, it would be a disservice to the importance Naraku Gospel places on them.