Stargazing: Shintoatsu Symphony - Asumi Kana
There's almost nothing normal about the world of Sasami-san@Ganbaranai. It may start off showcasing a young girl hikkikomori just spending her days indoors, but it quickly starts to incorporate stranger things like a city that turns into chocolate.
After the madness of every episode came to an end, the gentle background instrumentals were quickly taken over by frantic commentary and intentionally poor singing, just as part of the continuing gag. After spending so long wondering if there's actually a song behind the madness, the bonus blu-ray CD gave us a "clean" version by Asumi Kana. The episodic buildup just made it that much more memorable.