Dual! : Parallel Trouble Adventure - Special
Considering that I considered dual to be distinctly average I find it hard to believe the fans `demanded' an extension. Instead I think this exists as evidence that a `special', designed to capitalize on the expected success of the series, is done during the production.
I'm going to be a little bit careful to avoid spoilers for the end of the dual series. As a result this synopsis might seem a bit imprecise. Although, considering how basic the story in this is I don't think it will be a problem.
Effectively at the end of dual a change was made to the nature of the parallel worlds involved in the story. This effectively changed the status, and interaction, between many of the characters. While the nature of what type of change occurred was made clear at the end of the series we didn't really get to see what effect this would have on normal life, and some of the lesser characters. Thus the main essence of this extension is a somewhat self-indulgent look at the pleasant normality that follows the events of the series.
This also means that, by and large, nothing terribly dramatic or important happens. Sure, they try and build some dramatic tension with the re-appearance of a `lost' character. The one character who didn't make the transition to the `new' world, and whose coming could mark quite a change in the stability of the new world. But really it's not terribly interesting in practice and little is done with it.
So, in essence, we get to revisit all the cute characters from the television series as they form a proper tenchi-style harem. They fight, in their own way, over the male leads attention and affection while he does the innocent, un-perceptive and indecisive simpleton act. It's a carefully designed ploy to explain why there are some many females involved in the story, all ready for romance, without us feeling insane jealousy towards the male lead. Effectively we are supposed to see ourselves in his place.
But, while the ploy has power and looking at cute anime girls isn't too hard, this is a very poor specimen of such. Go and see tenchi, or a newer variant like Love Hina to see this formula done properly, in which each girl adds life to the mix and spice to the many well written interactions that result. This guy's hopeless and most of the females are pointless. The main reason for this lack of interest being the remarkably flat and un-inspired dialogue. And in this aspect, if in nothing else, it well reflects the series that inspired it.
In essence this short show has nothing to offer. It doesn't extend upon the story presented in dual, it doesn't add anything to the characters and it certainly doesn't develop any momentum of its own. The animation quality is pretty much that of the TV series, in other words not overly impressive. It doesn't match the cool animation of the first few episodes of the series and there's no action to speak of. The `cute' girls are offset by average character designs and a lack of `sparkle' in the dialog. The voice acting is acceptable but unremarkable, and the music is pleasant pop stuff.