K-On! wiki
K-ON! (けいおん!) anime is adapted from a Japanese four-panel comic strip manga written and illustrated by Kakifly. The anime adaptation is produced by Kyoto Animation and began airing in Japan in April 2009.
The title K-ON! comes from the Japanese word Keiongaku (軽音楽), literally ‘light music’, which means pop music in Japan.
The story revolves around four Japanese high school girls who join their school’s light music club to try to save it from being abolished, and their fun-filled learning and friendship.

K-ON! characters
Yui Hirasawa – the main character of K-ON!, she plays guitar. She didn’t know how to play the music instrument initially, but ‘accidentally’ joined the light music club. Yui has an easy going nature but when hyped, has incredible concentration… a genius in disguise?
Mio Akiyama – plays bass. She originally intended to join the literary club, but was forced into the light music club by her childhood friend Ritsu. Mio is timid on horror stuff and gets embarrassed easily, the reason she chose bass over guitar is to avoid being centre of attention.
Btw, guess where’s the name of this website was coming from?
Ritsu Tainaka – president of the light music club, drum player. She was the one who pulled everyone together into the club, but is often neglectful of her responsibility. She is a childhood friend of Mio, and has good rapport with Yui.
Tsumugi Kotobuki – a wealthy girl with a gentle personality, plays keyboard. She originally intended to join the choir club, but joined the light music club because the members are ‘interesting’. She has some weird special interest though.
Azusa Nakano – a junior member who appears later in the anime, plays guitar. Nicknamed Azu~nyan by Yui, she has mix characteristic from Yui and Mio.
Sawako Yamanaka – school teacher and advisor to the light music club. She was also K-on alumni, but she is trying to hide a ‘dark’ past.
Nodoka Manabe – Yui’s childhood friend and classmate. A member of the student council with mature personality.
Ui Hirasawa – Yui’s younger sister, mature and take care of Yui instead, and apparently a music genius in disguise too.
More K-ON! articles
K-on! all – K-on! wallpapers – K-on! videos
Information taken from Wikipedia.