During elementary school, Shizuno Takakamo and Ako Atarashi make friends with the recently transferred Nodoka Haramura. Upon hearing about her interest in mahjong, they take Nodoka to Achiga Girl's Academy, where Harue Akado runs a mahjong club for children. After a few games with Kuro Matsumi, Shizuno later tells Nodoka about Harue's history, including reasons leading to Achiga's club disbanding. By the year's end, Harue accepts an offer to join a company's mahjong team, which leads to the closure of the children's club. Nodoka also reveals that she is transferring out by next spring. The years have passed, and an excited third year Shizuno sees Nodoka on television winning the individual middle school tournament. Driven to reach the inter-high national tournament, Shizuno goes to Achiga's club room where she encounters Kuro, who had been maintaining the room since disbandment. Together, they revive the mahjong club with intent to meet Nodoka again. Instead of Bansei, Ako also enrolls into Achiga for the same reason.

Kuro takes Shizuno and Ako to meet her older sister, Yū, who becomes the fourth mahjong club member. The next day, Kuro asks her classmate, Arata Sagimori, a fan of Harue during her prime, and she joins as the fifth member. During the winter, Harue's company manga team had become defunct, and visits Achiga for some nostalgia. To her surprise, she finds Shizuno and the others playing. Wanting to experience the inter-high nationals once more, Harue decides to become the club's advisor and coach. With the mahjong club officially formed, the girls begin training for the prefectural preliminaries. Later in the evening, Ako encounters some of her former classmates who went on to attend prefectural rival Bansei High.

At the prefectural tournament, the Achiga team defeats Bansei in the first round and eventually qualifies for the nationals. To train for the nationals, Harue schedules the club to play against prefectural runner-ups. Immediately, Ako utters "Nagano", Kiyosumi's prefecture, as the first one to visit, and therefore, they play Ryūmonbuchi High. There, Koromo Amae overwhelmingly defeats Shizuno but doesn't discourage her or the team. Then, the excited team proceeds to defeat other schools at other prefectures. After a ten day training camp, the girls set off for the nationals. While stopping at a rest stop, Shizuno and the others meet Toki Onjōji and Ryuuka Shimizudani from Senriyama Girl's High, who are also seeded in the nationals. As the club finally reaches the nationals, they briefly walk pass Saki Miyanaga.

As the Achiga girls receive results of the drawing lottery, they find that they are on the opposite side of Kiyosumi while on the same side as the top-ranked Shiraitodai High School. As the girls do some research on their opponents, Harue meets up with her former coach, Kumakura. On the day of the first round, Achiga is pitted against Sanomo, Urabandai and Imizusougou. After some initial difficulty, Kuro manages to show off her dora-drawing skills in her round, and Achiga soon sails to victory and advances to the second round. Later, Senriyama read up on Achiga's victory, preparing to face them in the next round, along with Koshigaya and Kentani. As Kuro enters the competition room, she encounters a waiting Toki.

As the vanguard match begins, Toki's ability to see one turn ahead puts pressure on Kuro, whose dora-style renders her defense play weak and predictable. Adding riichi with her ability, this enables Toki to dominate the match, and Kuro is left ineffective. With Kuro in tears, Yū steps into the second match motivated to get back the points Kuro lost, while Senriyama hopes to use the information they gathered on her against her.

As the second match begins, Yū starts off well but soon struggles when Senriyama's Izumi Nijō figures out her play style of picking warm tiles with red characters. However, Yū makes a comeback as Izumi fails to observe that the tiles Yū draws include any which feature the color red. Then the third match is played out with Ako against Senriyama's Sera Iguchi. She manages to bring Achiga up to second place.

During the fourth match featuring Arata, some tough competition puts Achiga back into third place behind Kentani. As it comes down to the last hand of the final match, Shizuno faces tough odds. However, her determination to not give up gives her the opportunity to get back into second place, allowing Achiga to proceed to the semi-finals alongside Senriyama. As the girls celebrate their victory, Harue warns that in the semi-finals, they'll not only be facing Senriyama, but Shiraitodai as well. As the girls go out to eat, they spot Harue with Kumakura, who is talking with her about potentially joining the pro circuit again. As the girls start worrying that Harue may abandon them, they run into Tsuruga Academy's Momoko Touyoko and Satomi Kanbara.

Satomi brings the Achiga girls to her grandmother's house where they meet Tsuruga's Yumi Kajiki. Wanting to improve their skills and become stronger, the Achiga girls ask to train with them. Since they are not participating in the individual tournament, they are also allowed to battle against Kazekoshi Girls School's Mihoko Fukuji, and they soon come up against some national level play. The next day, the girls meet up Kei Arakawa and several other talented players to continue their training, whilst Kiyosumi play out their second round match. Later that evening, Shizuno spots Kumakura and confronts her about her discussions with Harue. To her relief, she learns that Harue turned down the offer of going pro, saying that she wants to stay with Achiga til the end. As Shizuno breaks the news to the others, they become determined to win the semifinals, where they face Shiraitodai, Senriyama and Shindouji Girls' High. The first round soon kicks off, with Kuro preparing to face off against Toki, Shindouji's Kirame Hanada and Shiraitodai's strongest player, Teru Miyanaga.

As Toki makes the first winning move, everyone starts to feel the strange power of Teru, who soon starts a winning streak that even surpasses Toki's predictions. Toki recalls the time when she was picked to be Senriyama's ace, where she revealed to Ryuuka and Sera the prediction ability she got following a collapse. Toki soon regains her confidence and helps Kirame disrupt Teru's streak. As the third South Hand begins, Teru looks set to restart her streak whilst Kuro laments that she hasn't been able to do anything.

Nodoka has a dream where she meets up with Shizuno and the others and ponders about its meeting. Meanwhile, the first half of the vanguard match finishes, with Teru still ahead, although the Achiga girls manage to figure something out about Teru's play style which they pass on to Kuro. Teru continues to dominate the second half, managing to get a 100,000 point lead over Senriyama, when Toki recalls when she previously attempted to look two turns ahead and ended up collapsing. Having secretly practised at home, Toki decides to put her double turn peek into practice.

Toki uses her ability to look two turns into the future, enabling her to stop Teru's streak but leaving her extremely weak in the process. Meanwhile, Kirame recalls how her team chose her to be the sacrificial pawn owing to her purported ability to never go bust. As the game approaches its climax, Toki is left incredibly weak and is supposedly unable to use her ability. Meanwhile, as Saki, Nodoka and Yuki arrive at the arena, Saki appears to be preoccupied with something. As Toki remains under pressure as Teru decides to prolong the match, she recalls how her teammates supported her during a training camp. Determined to help her team, Toki decides to take a risk and attempt to look three turns into the future.

As Toki pushes her body to the limit to look three turns into the future, she predicts Kuro is finally about to make her move. As Kuro is pressured into potentially discarding a dora, she recalls her friends and her late mother and decides to discard a dora, throwing off Teru's calculations and enabling her to earn some points off Teru, bringing the first match to an end. Just then, Toki collapses from her fatigue and has to be rushed to hospital. As Achiga prepares to move on to the next match, they finally run into Nodoka, both promising to do their best to reach the finals. With their resolve in place, Yū enters the fray for the second match.