When you think about it, Mushishi is almost like a subtle satire of the premise of some reality shows. The typical progression in those shows is that they call in the awesome investigator guy, he always knows what to do, and he always leaves everything neatly squared away, but in Mushishi, the typical progression is that the awesome investigator guy looks at the problem, knows exactly what to do and gives advice, and then his clients totally ignore him because they realise that all along they'd actually loved their problem, thank you just the same, and the awesome investigator guy just shrugs his shoulders and walks away.
Though on second thought, the same comparison could probably apply to almost any show that plays The Hunter a little too straight.
In episode 6 of Zoku-shou, when we see the flashback about the cherry blossom girl, you see the sister in the original family that found her. You only see her again when the kids are adults when the father dies, and never again. Now, since the little girl went to live with the brother, it could just be that the sister lived elsewhere so we just don't see her again; but given what the family has been doing to keep the girl alive...