The limited first pressing for K-ON!! BluRay Volume 9, the last volume of the K-ON!! BluRay releases has ranked #1 on Oricon's sales chart for two consecutive weeks. It did so by selling an additional 10,000 copies (rounded to the nearest thousand) during the March 21-27 week.
The ninth volume is also the third one in a row and the 10th one in the franchise to rank #1. The K-ON! franchise now holds the sole record for the most #1 Blu-ray Discs of any anime, after sharing it last month with Macross Frontier (nine #1s).
The last volume of the BluRay contains the last episodes of the anime which depicts the last few days of Yui, Mugi, Ritsu and Mio as members of the Light Music Club. Asides from that, it contains extras exclusively available in the official BluRay release.
Source: Mantan Web via Anime News Network