Season 0 of K-ON! premiered on June 26, 2009.

Season 1 of K-ON! premiered on April 3, 2009.

It's Yui Hirasawa's first year in high school, and she's eagerly searching for a club to join. At the same time, Ritsu Tainaka, a drummer, and her friend Mio Akiyama, a bassist, are desperately trying to save the school's light music club, which is about to be disbanded due to lack of members. They manage to recruit Tsumugi Kotobuki to play the keyboard, meaning they only need one more member to get the club running again. Yui joins, thinking it will be an easy experience for her to play the castanets, the only instrument she knows. However, the other members think their new addition is actually a guitar prodigy...

Season 2 of K-ON! premiered on April 7, 2010.

It's the final year of high school for Yui (guitar), Ritsu (drums), Mio (bass), and Tsumugi Kotobuki (keyboard), the founding members of the Light Music Club. Together with junior member Azusa (guitar), they spend their days in the music room enjoying tea, sweets, and practicing music. Amidst band practice, preparations for the new student orientation performance, scouting for new members, they still have time for "After School Tea Time". It's a delightfully fun time in K-On!