The seven Blu-ray disc volumes of K-ON! have an extra short anime "Ura-ON!"

With his mother dead and his father working abroad, Futami Nozomu returns to the town where he lived as a child, to attend high school and work part-time at a local shrine. He soon finds himself caught up in a local legend of twin girls loving the same man. And there are many twin girls in this town.... (Source: ANN)

The Futaba Detective Agency, being run by Rentarou, who has taken over the family business, after his father's death 3 weeks ago. Along w/ Sara & Souju, his live-in identical twin assistants. He ends up running afoul of the local Yakuza. (Source: ANN)