Y: The Last Man, Vol. 4 Safeword

There are two principle story arcs in this volume. The first, Safeword, deals with the issue of Yorick's survivor's guilt over being the only survivor of the plague. He does this only after Agent 355 drops him off with another Culper Ring agent, who breaks him down psychologically in order to have him face his issues. It's not the type of psychology that would work in the real world, but desperate times and all that.
The second story deals with an encounter with a militia group, and really highlights a theme that Vaughn has been working with throughout the series: that a lot of the differences between males and females are the result of cultural and social factors, rather than inherent sexual differences. Of course, he tends to do this by showing that women are capable of being just as pig-headed, violent, and selfish as men are, but there are moments in here where he does so by placing them in more noble circumstances as well.