K-On! Ura-on are bonus episodes from the anime K-On! and they used a different kind of animation or drawing style.
This is the first time I've ever encountered such style (very different compared to the series, though you can easily tell the resemblance to the original) and was wondering for this style's name, if it have. Also, did other anime used this prior or after K-On! Ura-on was released? And, what is this style's history and background? Or is this just created to be unique or random reasons by the K-On! production?