First and foremost, as what other manga readers have mentioned, ep18 deviated significantly from the manga and the novel. What can be interpreted, then? The most obvious would be that the anime series will end in a different path from the manga, as there is already a bifurcation between the path of the manga and the path of the anime. Whereas in the manga Yamazaki is not included in the tomfoolery of Kobayashi, here in the anime he is. Further explication on their return of the goods with the cooling-off period can only be found in the anime version of the series. The return had not been shown in the manga and we are shown an even more withdrawn Satou (that is, until the later chapters). Misaki was fooled by Kobayashi in that arc of the manga - resolution was non-existent, however.
In ep18, although they were very much fooled, and fooled twice they have managed to catch Kobayashi at her house (with some precise throwing done by Satou, no less
) unprepared with her bag of tricks. Devastated, Kobayashi gives them the return papers and the reason (very pathetic) why she has been trying to mulct them of their money in any way possible until they hear an inhuman noise upstairs which causes her to stop and try to mask this noise as the noise made by her 'pet.' The group, both curious and disquieted then venture to seek the truth to what lay above them, and they discovered it to be her brother and Satou's online teammate. This is a story highly different from the manga - the manga didn't have such explication as to why she has been doing unscrupulous stuff, and it certainly didn't tie her reasons with the existence of her
hikkikomori brother. This was a very wonderful move by GONZO, to which I applaud them (despite what others may say).
What does this mean?
It either means that the finale (or the producers) is setting Satou up for an even greater and more painful fall (this scenario is highly abhorrent to me), or setting the plot up to end in a redemptive manner (this is what I'd prefer). I already trust what GONZO could do with still running material, like Gantz, for example, and although I felt a little disappointed at the sad ending I loved how they ended it (albeit tragically) on a note of spiritual redemption.
I know this series isn't for those with more escapist tastes as this series jars one into facing realities much worse than most of us are experiencing here, but if the producers had the foresight to develop an entirely new ending for this wonderful series starting with these major changes I applaud them - they did it too late with Gantz although I have also heard that although Last Exile wasn't really properly concluded when it was airing as an anime series they've also made a conclusion fitting for it.
Although a happy ending for these long-suffering characters may sound and seem cheesy to many, unless one's a total sadist and a nihilist, one wouldn't want to see these characters suffering permanently. Let them have a ray of hope in a world like this.