Usually, a filler episode on an anime with a nice streaks of great episodes dampens the enjoyment. But there are rare instances where this filler episode is so enjoyable it’s just feels it was necessary for future episodes. In the case of Kurenai, I think it was needed for Murasaki’s sake. She needs to have fun and act like a child should. So, they allowed her to be in a musical!!
This episode was really funny! I seriously couldn’t stop laughing at the bad singing and exaggerated movements, which added to the hilarity. The practice scenes were funny enough, but once they actually got singing, I might as well have been rolling on the ground!
Ah~! What’s better than watching a voice actress teach a singer how to sing! ^_^ Priceless!
Open Your Mind 
LOL, I found the practice scenes funnier than the actual ‘musical’ (which looked a tad bit grotesque, but that was probably done on purpose anyhow). Sawashiro Miyuki tutoring Shintani Ryoko was worth the episode enough already XD
That episode was truly awesome! The good and bad singing was pretty cool, especially knowing that both Sanada Asami and Sawashiro Miyuki are fairly good singers and that Shintani Ryoko is (in general) well above average for a seiyuu with a music career (Wonderful World is a great album btw). Kinda bummed that Kurenai is slated for only 12 episodes or so. :(