She is portrayed faceless (covered by a crystal), and wears a whitehooded dress over a blacksleeveless dress. In-game, they give access to the Forgotten Hall and Memory of Chaos game modes.
Note that the appearance applies to persons associated with the Garden of Recollection: the Messenger should not be confused with Memosnatchers (Danbooru post #8822199) if she is depicted in the Astral Express.
