Kagura's name comes from Shinto ritual: the kanji for Kagura (神楽) meaning "entertainment of the gods". It was used to describe the traditional music played at shrines and the Imperial Court. Kagura also makes a cameo appearance as an anthropologist in Classroom of Thesis; From the Report to the Graduation Thesis by Kazuhisa Todayama which refers to several other Azumanga Daioh characters.
While she makes appearances earlier on as one of Nyamo's students, Kagura doesn't become a true acquaintance of the group until sometime later, joining Yukari's class in the 2nd year (Yukari selects her as a ringer to win the school athletic competitions). She devotes most of her time to the swim team but is an all-around good athlete. Thanks to her dedication to swimming Kagura receives some rather pronounced tan lines during the summer months, which friends like Osaka waste no time in pointing out.
She also has a one-sided rivalry with Sakaki and attempts to outdo her in all things, be it playing softball, sprinting, or even eating lunch. This is how her character was introduced to the rest of the cast, when during 1st year's field day, she was defeated by Sakaki in a running event. The next time the two meet, Kagura has decided to make Sakaki her rival, yet she also makes continuous attempts to be a good friend to Sakaki. Unfortunately for her, Sakaki is a natural athlete (and doesn't remember a thing about running against Kagura during the first Athletics Fest, which stuns Kagura) and defeats her in almost everything except stamina events. Like her would-be rival, she is sometimes embarrassed when Tomo calls attention to her large breasts.
(Source: Wikipedia, edited)
