Well, I had to write this review to try to convince you, dear reader, to ignore the review below me. There is a story, and I think the plot flows very naturally. On top of that, there is some very nice art, intelligent writing, and decent pacing in this manga.
Binetsu Kuukan is a relatively realistic take on step-sibling romance. The two main characters are both reasonable people who are obviously attracted to each other, but who also care about their parents and are loathe to ruin their delicate family balance. You get the picture, I'm sure. These two down-to-earth characters who try to deal with their forbidden love in a levelheaded manner are more interesting to me than most characters in series like this (who are usually blinded by love and make one stupid decision after another.)
Of course, this is still not the most original premise in the history of manga, but it's well executed. In contrast to what the review below me claims, I do not think the developments are forced (I don't know how SoleSoul expects them "not to interact with each other" when they live in the same small house...) On the contrary, I think this delicate situation escalates at about the pace you'd expect given they're unavoidably attracted to each other and literally can't avoid seeing each other every day. This is a reasonable story, that is further supported, like I mentioned, by exceptional art and smart writing. If the premise sounds interesting to you, don't let the review below me stop you from trying it. Binetsu Kuukan is quite good.