Board Thread:Questions and Answers/@comment-24822455-20140416023246/@comment-6697950-20150415165636

The anime is based on the book. The book never even mentions Sachi in the 4th arc, so there's no chance that she will be mentioned in the anime either, as she's not relevant to the plot of the arc. And the dead don't go to a virtual world for their after life. Underworld is a reference to Alice in the Wonderland, not to the place where the dead go.