I decided to watch this because it's only 10 minutes and it earned high scores, for the most part. Plus, I'm kind of a sucker for obscure anime and manga.
Story: A young girl tells of her meeting with the black swordsman, a mysterious man who loves to read books. That's really the gist of it, but it is very well-executed. Actually, it would be well-executed even if this wasn't 10 minutes long. Since it is, it is freaking incredible.
Animation: A feast for the eyes. The grayscale backgrounds look like photographs, and they clash nicely with the minimalist, sketchy characters. The occasional shot of color makes for an interesting art style, but it is certainly gorgeous, and fits the mood perfectly. The animation is lacking, but it adds to the feel of the OVA and fits with the artwork.
Sound: The OST is really just one very pretty song which fits quite nicely. Since there are only two characters, the seiyuu don't have to do much, but the lack of emotion is portrayed well. There is no OP and no ED, of course.
Characters: One cannot expect character development, but the characters seemed to have more depth than many characters from much longer anime. The dynamic between the characters was touching, and once even funny.
Overall: Despite the name, this is a dark anime which is worth a watch. Its length makes it a good anime for even the most hurried person, and the quality is stunning.