Board Thread:General Discussion/@comment-6986530-20170327230407/@comment-4698889-20170410001341

We know that Ma planned to transfer Levia into Postman's body, so that's the implied reason why she's a Rin.

As for Waiter, I'd also like to point out the parallel between her and Rin Miroku, in that they're waiting for their "counterparts". For me personally, I think it's safe to assume that the Graveyard waiter is, in fact, the Waiter in Evil's Theater that we all know and love.