When Yuuta Asamura's father remarries he gains a stepsister, Yuuta Asamura, who is slightly younger than him and is the prettiest girl in their school year. Early on the two decide that it is best to keep their distance from each other as they feel getting close could make things awkward for the family. Of course they can't totally avoid each other.
I thought this series was okay if not the most original. It is the sort of series that is fun enough while watching but you know that soon after it finishes you'll forget all about it. In fact writing this now I'm struggling to think of many details of the show! The characters designs and animation are decent enough. Overall I'd not say this was a must see; perhaps give it a try if you enjoy the genre. At least now one can watch the whole series rather than having to wait a week for the next episode.
These comments are based on watching the series in Japanese with English subtitles.