The story is centered in the two main characters: Koshiro, who is a 27 year old man, and his 15 year old sister Nanoka. At the start of the story, neither one of them know each other, as a result of their parents divorcing when Nanoka was just a toddler. Koshiro lived with his father, and his sister went away with their mother. About ten years later, the two of them meet in the train. Unknown to them that they are siblings, they end up going out on a date. When they finally discover the truth, Nanoka is happy to have an older brother, but Koshiro can't stop thinking of her in a romantic way. To make matters worse, their father tells Koshiro that Nanoka will move in with them, since her high school is closer to their home.

Even though the story of sibling falling in love is not a new concept to the anime world, this anime was beyond everything I expected. The emotions portrayed are so realistic, it is easy to relate to the characters and their feelings. The theme of the anime itself makes is not suitable for everyone, but the way the anime was made is so realistic and serious, it's hard to tell who this show is targeted to. There are a lot of occurrences that are for mature viewers, but this does not make it hentai or ecchi at all. It is also a very confusing story, because they love each other so much, the viewer starts to hope that they can be together in the end, somehow. I cried like a baby at the end of the story, and I can say this much: I went through all the emotions known to man watching this series. But even though it left an unsettling feeling of uneasiness, I have to admit I really loved it.