Miruchi and Yuka, during the middle of the series, are grade-school students and good friends of Chiyo-chan, but were separated when Chiyo advanced to high school. Occasionally, though, the three would meet on the way to school and exchange stories about their experiences. Near the end of the series, though, both Miruchi and Yuka had advanced to middle school and proudly showed-off their new uniforms to Chiyo, as well as Sakaki (who was walking with Chiyo at the time). If one were to look closely, Miruchi resembles a younger Minamo Kurosawa (Nyamo), while Yuka is a younger double of Yukari Tanazaki. (Source: Absolute Anime)

Ten year old child prodigy, Chiyo Mihama, is finding it tough fitting in at high school with the girls five years her elder: Osaka (dimwitted with a weird take on the world), Tomo (a powder keg that goes off at a moment’s notice), Kagura (the competitive athlete of the bunch), Yomi (the hothead), and Sakaki (timid and obsessed with a love of animals that isn’t reciprocated). Together with their teacher, they navigate the rough waters and fun times of high school. 
 
(Source: Sentai Filmworks)

It's not manga, it's Azumanga! &minus; smart, fun and totally addictive. Created by the iconoclastic Kiyohiko Azuma, Azumanga Daiou is strongly character driven, taking the reader through the daily tribulations of Miss Kurosawa, Miss Yukari, the wild Tomo, hair-triggered Yomi, ditzy Osaka, brash Kagura, cute Chiyo-chan and athletic (but girly) Sakaki. 
(Source: ADV) 
Notes: 
- A great number of chapters are divided into several parts that have been included in the final chapter count. 
- The chapter count includes 5 extra chapters.