Momoko is Yumi's friend, and a high school first year student. She has a lacking presence, and is often ignored by her friends despite her efforts to gain attention; as such, she soon gave up on building relationships with other people. After a match through LAN mahjong, Yumi acknowledges Momoko's skills and finds her; the two become friends afterwards. Her mahjong playing ability comes when she augments her negative presence into an advantageous stealth state, causing her opponents to miss her moves. 

(Source: Wikipedia)

Miyanaga Saki is a first year high school girl whose family would get angry if she won the family mahjong games. But losing would also have its consequences. Because of this she develops a new way of playing that allows her to stay on the thin line between winning and losing, the plus/minus zero score, an almost impossible score. In a game that relies mainly on luck, the plus/minus zero score is harder than winning, but Saki can achieve this every time. Having always hated the game, her friend from middle school, Suga Kyotoro, forces her to play in the schools mahjong club. Her developed skill and superhuman luck has made her a worthy mahjong opponent, even to the middle school's national mahjong champion. (Source: Anime News Network, edited)

Saki's never been a big fan of mahjong. A lifetime of being forced to play with family at holidays (and losing her money as a consequence...) has left a foul taste for the game in her mouth. When she's convinced, though, to play a game with her classmates, she discovers that not only has fending off her family left her with an uncanny ability for the game but, more surprisingly, that it can even be fun!
 
Is this revelation enough to cleanse Saki's distaste for the game? Can her classmates convince her to join their club, or is there just too much baggage to make it worth her while?
 
(Source: Yen Press)

The Achiga Girls' Academy in Nara once defeated regional mahjong powerhouse Bansei High School. It advanced into the national team semifinals but lost to the eventual champion, and the mahjong club was later disbanded. 
Six years later, elementary school student Shizuno Takakamo befriends transfer student Nodoka Haramura. The two eventually enter Achiga Girls', but Nodoka transfers out of the school in the second year. 
When Shizuno sees Nodoka on television the following year as the national middle school individual mahjong champion, she decides to revive Achiga's mahjong club.

After their success in the regional tournament, the Kiyosumi High School mahjong team faces off against a whole new level of competition at the National Tournament in Tokyo. (Source: Anime News Network)

The Achiga Girls' Academy in Nara once defeated regional mahjong powerhouse Bansei High School. It advanced into the national team semifinals but lost to the eventual champion, and the mahjong club was later disbanded. Six years later, elementary school student Shizuno Takakamo befriends transfer student Nodoka Haramura. The two eventually enter Achiga Girls', but Nodoka transfers out of the school in the second year. When Shizuno sees Nodoka on television the following year as the national middle school individual mahjong champion, she decides to revive Achiga's mahjong club.

Specials included in the DVD volumes 3 through 9 and Blu-ray Box that recounts stories that take place before, during, and after the first season of the anime.
 
(Source: Saki Wiki)

A single episode OVA released with the 14th volume of the Saki manga, consisting of 4-koma gags featuring characters from the first season. The two pros meet up at a family restaurant. The captains of the four teams prepare for a joint training camp. Ikeda keeps her little sisters occupied. The Tsuruga team goes on an unplanned camping trip. Ryuumonbuchi celebrate Koromo's birthday.
 
(Source: Anime News Network)

In the 8th Saki spin-off project, Saki and the other first year members of the Kiyosumi High School Mahjong Club are recommended a new way to enjoy mahjong--through the video game, FINAL FANTASY XIV!
 
(Source: MANGA UP!)
 
Note: Includes chapter 0.

Side stories of the "Saki" manga in 4-koma format. 

Note: Chapter count includes 7 omake chapters, 1 from each Volume.

Special chapters of Saki Biyori serialized in Big Gangan.

Saki spinoff focusing on Someya Mako as she cooks meals for customers of her family's mahjong parlor. 
 
(Source: Japanese Publisher, translated)

Momoko Touyoko