This is a series I just re-watched. I still enjoyed it, it's fairly good. However, there are some overall issues with No. 6 that make it average, with my seven rating slightly due to the fact I love characters with white hair and red eyes. First off, if you absolutely hate any sort of Shounen ai vibe, don't watch this. Second, it's only eleven episodes, so you can already assume that the plot won't be perfect.
Story 6.5/10:
With a bit of sci-fi, slight vibes of Shounen ai romance, and the whole topic of 'utopian society never being a utopia', No. 6 creates its story. Shion, the main character, meets Nezumi, and they try to find out what No. 6 is really trying to accomplish by implanting people with parasitic wasps...well Nezumi just wants to destroy No.6(but anyways). It was acceptable as a plot premise. However, (as you may have guessed) the eleven episodes did not unravel all these mysteries, and though several were solved, there were still a variety of questions about the plot left unfinished. The ending itself was put together well enough, but was still slightly annoying with the typical 'this is really just the beginning' end when not everything about the plot made sense. The middle consisted of continuing the main plot while being introduced to minimal side characters (yay :D not too many characters) and developing the relationship between Shion and Nezumi. More emphasis should have been put on Safu's character if she was going to be more important to the plot later. Nezumi and Shion got some relationship development together, but it still could have been stronger. I'm glad they did't try to add a Nezumi and Shion romance in instead of just hinting at it, because then the plot would have been even more rushed. A big part of it had to be the length of the Anime, it just wasn't enough to clear up plot issues and get really solid character development. Overall it was enjoyable, but definately needed a few more episodes.
Animation 9/10:
Not very picky about this, it was good enough for me, they even did okay on the dogs. I've actually seen some pretty bad/creepy/weird looking animals (especially horses) animated. Of course, both Nezumi and Shion look very cute.
Sound 7/10:
It wasn't bad, but I didn't like the opening or ending. Average I suppose. When a song slightly important to the main story was sung, it was done in a very lovely voice, so that was a nice touch and fun to listen to.
Characters 7/10:
The characters were fine in most respects. Shion was my favorite, white hair red eyes, typical nice guy who's innocent because he lived in No. 6, but has an interesting tendency to get violent/snap if anyone hurts Nezumi, that was a nice touch. Of course, after he learns what No. 6 has really been up to he (naturally) gets upset, but that was another part where I though there needed to be more time spent on. As the main character, I don't want him mentally wimpy all the time (those characters annoy me), but he recovered so quickly from shock after shock of things that could possibly make someone psycho. The Anime needed to create a darker atmosphere(plot was dark material, but didn't seem to have a dark enough atmosphere at times), and create a pacing so that what the audience and Shion 'discovers' about No.6 is more impactful. Nezumi was ok, but seriously pick a side, does this guy believe the ideals he yells at Shion all the time, or does he (secretly) want to believe the unrealistic, and naiive dreams/opinions Shion holds!? He got angry at Shion all the time for his unrealistic views/innocence, but he didn't even follow what he said himself, and seemed like he would rather go with Shion's point of view. Safu is that one girl that is in complete love with the main character and would do anything for him, and she likes her grandmother, that's it. Of course this is all unrequitted lover on her part because of the Shounen ai vibes between Nezumi and Shion. Mother character who loves Shion (hey at least she's not dead), Inukashi and Rikiga who both needed to get fleshed out more, but end up helping Shion. Still, the characters fit well together and weren't dislikeable. To me, Nezumi and Shion's interactions were better than the overarching plot. Most of the characters were interesting because they possessed some original traits.
Overall an enjoyable watch for anyone who likes a sad plot, the utopia theme, interesting characters, even though the plot left unanswered questions. NOT if you're looking for great Sci-fi, if you wanted Shounen ai(there was only 'vibes' of it), or if you DON'T want those 'vibes'. xD (frankly I expect this from short Anime, it's either 'really rush the plot, simplify the plot, change the plot, abruptly end the plot, hope for second season to finish plot, or leave holes in the plot'. None of these are good things normally :'( Sad reality of Short Anime. Which do you prefer?)