This episode represents a significant departure from the rest of the series so far. It contains a lot of firsts for the series: the first hints of tension between Ginko and another human, the first time Ginko's lack of knowledge has been given a focus, and very notably the first time Ginko outright fails to help someone (though that is best attributed to the patient, not him). But perhaps more important than any of these is the first direct statement of one of the series key themes: coexistence.
The first hints come with the realization that the Imeno no Awai are helpful and destructive at once. They just as easily cause landslides that destroy homes as they do wellsprings that help the village expand. They aren't enemies (or at least they don't have to be), nor are they necessarily friends. They, like many of the mushi throughout the series, are just other creatures, living. As Ginko says, no one is really at fault - there aren't good or bad sides.
The most interesting thing about the theme, though, is how. . .painfully it is portrayed. Jin loses his wife, friends, and indeed his entire village to the Imeno no Awai. While there was a possible prevention for it - taking Ginko's medicine exactly as instructed - given how little information he had, it was hardly unreasonable of Jin to act as he did. After he does learn the truth, there is still no true solution to his problem - at least, none Ginko knows of - and no recompense for his pain. Despite having lost everything, Jin is still shackled by the mushi.
This is where things get most curious. Coexistence is typically shown as a kind, loving affair where people choose to get along and live happily amongst each other because of it. Here it is presented as a harsh fact of life. There is no choice; you must coexist, or you will live a tortured life and lose everything, from your loved ones and home to your very peace of mind. In a way, it's a perfect tragedy; nobody does anything wrong and everybody still loses.
This has raised an interesting question for me. I'm well aware of how often the show stresses the importance of creatures cooperating with each other, but I realize I've no clue the underlying reasons for it. Is it as I previously thought, and the reason for coexistence is because it is a wonderful thing full of hope? Or is it simply that it's a fate forced upon us, and we have to make the best of it or suffer the consequences? At this point I'm thinking it's a little of both, but I suppose I'll have to watch on to tell.
As an aside, I think Ginko was what surprised me the most in this episode. Where Jin and the Imeno no Awai are tragic entities, Ginko is a manipulative puppeteer, and not a very good one at that. His lies (half-truths might be more accurate), whatever the intentions, are more influential on Jin's catastrophic actions than anything else, and though he always has an idea of how to solve the issue, none work. In a way, he best fits the archetype of a villain seeking redemption; he, more than anything else, was the cause of the problem, and now he's trying to fix it. That he fails miserably at doing so is in keeping with the episode's bleak outlook, but has implications beyond - Ginko carries on in spite of these events. Whether that simply means he's hardened or something else, it certainly adds a darker side to his travels that the audience rarely sees.
Snippettee went all out and used this episode as the jumping point for an existential discussion on dreams back last February. A fun read, if you're into that particular brand of philosophy.