Its full title is “Fire Emblem Echoes: Shadows of Valentia Memorial Book Valentia Accordion”. If the naming convention didn’t clue you in, it’s from the same people behind the Tellius Recollection books and is advertised as the 3rd memorial book in the series.
The reason we’re bringing this up again is that the cover for the book has just been revealed on Amazon Japan. Otherwise, that’s still all we know about the book, other than the fact it’s priced at 3,780 Yen and has 256 pages like the other memorial books.
Anyway, the text on the cover is all familiar stuff. The blurb in the corner states that Intelligent Systems has supervised the contents and that we should expect previously unreleased information, as well a look at the past and future of the Valentian continent.