Where to begin with this one....where to begin. Guess first is that this is by far not a record breaking anime; nor is it award winning. For that matter, it is not even "average", which is a bit of a shame, really.
The story is about a teen (with a tragic past) named Junna whom one day encounters someone whom he has never met claiming to be his sister, yet he already has one. He calls/says this stranger's name, and the mystery starts from there. Who is she? Is his sister really his sister, or an elaborate imposter? Is the stranger confusing him for someone else? Is this an elaborate plot for her to become closer to him?
Unfortunately, these questions are never answered until the extremely latter parts of the series; around episode 9. The rest of the time is devoted towards them living an average school life with the girls flaunting over their brother, aside from the one beach episode. By the last bit, it is finally revealed that while a young child, Junna was given a magical wish granting device, to which he used to bring Senna (a sister whom died in childbirth) into his world; causing great havoc. After some deliberation/thinking, Junno, Haruhi (the stranger), and Senna use the device to wish for a world where they are all alive and well.
The animation was not bad at all, which was a boon. However, the occasional bits of CGI and actual video clashed heavily whenever they appeared, making the viewing very awkward. The musical score was alright as well. While typical sounds were used, it did not really subtract much from the series...though the hearing of a constant "Onii-chan~!!" got a bit annoying after a while.
Not much in the way for characters, unfortunately.
The story has several weak spots that are a bit nonsense.
Overall enjoyable. I think it helps that they are shorter episodes.
The pacing is good.