This is the last volume.
No doubt, it was a surprise to all the fans. A lot of the small and big mysteries are not explained, but that probably doesn't matter. This book is apparently a journal describing the end of the human race. Even that fact came as a surprise to me, even though I believe I was aware of it subconsciously. It's a peaceful end, though, which is what the author is wishing for, if I'm not mistaken.
The last page sums it up nicely. "hito no yoru ga yasuraka na jidai de arimasu you ni."
