The Auditors of Reality cause the Apocalypse, and Death and the other Four Horsemen respond by riding out against the Auditors, FOR humanity.
Exactly. Only, while it is true we have to ride out, Death added, drawing his sword, it doesn't say anywhere against whom.
Earlier, Susan asks him if he really thinks the Apocalypse will happen and the Horsemen will ride out, because no-one really believes in that stuff anymore. Death replies that he does, and that's what's important.
Myria LeJean meets Death after having earned a soul.
Near the end, Lobsang makes the cherries of the monastery trees (which are always in bloom) ripen, as a gift for Lu Tze who had briefly considered that it'd be nice to pick cherries for once at the beginning of the book.
Another near the end, when Susan and Lobsang have their perfect moment.
While Madam Frout doesn't understand Susan's teaching methods and tries to suggest she adopts Learning Through Fun method instead, sometimes she hears a mental voice of "Miss Frout, who had been quite a good if rather shy teacher ... whistling and cheering Susan on."
Also, Susan checks if Madam Frout has been drinking lately, and is "pleased to see that the old girl was going a bit easier on the stuff".
The fact that Death, essentially, gets Susan in on the plot so that she can find someone like herself and not be so alone in the world. He really does care.
There's something sweet about Susan finding out about Wen and Time, or at least how the narration puts it. "Time waited for no man...Perhaps she had waited for one, once."