Yoko and Osamu Sonoyama are a childless couple who adopt a boy named Hitori... or so they believe. 'Hitori' is actually a pair of twins, the eponymous Migi & Dali. The two didn't think anybody would want both of them and they fear being separated. They play the role of Hitori with one of them in the open, the other nearby, and switching places when they aren't being observed. They are also on a mission; their mother had been murdered and they are determined to find out who did it; they are sure the killer lives in the village where they now reside.
I thought this was a good series; quite different to most series. The central conceit may be a little unlikely but it proves to be interesting. Rather than playing the idea for laughs we get drama that provides genuine tension, especially towards the end. The character designs are impressive; subtle differences make it possible for the viewer to differentiate between the twins. Overall I'd recommend this to anime fans looking for something different.
These comments are based on watching the series in Japanese with English subtitles.