“Cagayake! GIRLS” by Sakurakou Keion-bu (Aki Toyosaki, Yoko Hisaka, Satomi Satou, Minako Kotobuki)
used as OP for episodes 1 – 14 (including OVA).
Surprised? Outraged? Trolled? Angry? Pleased?
When I said I love voice actresses doing the recording for OP and ED, you guys should realize that a K-ON! song would be high up on the list.
No matter what you think about K-ON! (for example, I generally dislike pure comedy and moe), K-ON! OP is a perfect reflection of its anime: cute girls doing cute things and making some music if they feel like it.
Also worth mentioning is the ending “Don’t say ‘lazy'” by Sakurakou Keion-bu, and in the second season, opening 1 “GO! GO! MANIAC” by HTT (Houkago Tea Time).