K-On! (けいおん！） Is a Japanese four-panel comic strip seinen manga written and illustrated by Kakifly. The four main characters in the beginning of the story are Yui Hirasawa (Guitar), Ritsu Tainaka (Drums), Mio Akiyama (Bass), and Tsumugi Kotobuki (Keyboard). Later, Azusa Nakano (Guitar) joins the Keionbu (Hence the anime's name, K-On!).
K-On! Was a wonderful Manga/Anime! I want to watch the entire series again!