Ako Atarashi is a first-year high school student at Achiga Girls' Academy and one of the central figures in its mahjong club's revival. Her journey is deeply rooted in a childhood friendship with Shizuno Takakamo and Nodoka Haramura, with whom she first learned to play mahjong in a local children's club at Achiga. At that time, she was considered the second-best player among the children. However, when the club disbanded, Ako chose a different path from her friends. Driven by a serious desire to improve her skills, she attended a different middle school specifically for its strong mahjong program, leading to a period of separation from Shizuno and Nodoka.

Despite this separation, the bond of their shared passion for the game remained strong. When Shizuno decided to restart the Achiga mahjong club in high school with the goal of reaching the national championships, Ako was quick to rejoin the effort. In a significant decision that underscores her dedication to her friends, she turned down an opportunity to attend Bansei High School, a known powerhouse for mahjong, to return to Achiga. Her primary motivation is not simply victory, but the desire to once again experience the joy of playing mahjong with her old friends, especially Nodoka, on a grand stage.

Personality-wise, Ako is cheerful and sociable, sharing Shizuno's energetic disposition but typically balancing it with a more logical and pragmatic outlook. This grounded nature makes her a reliable counterpart to Shizuno's more impulsive enthusiasm. Harue Akado, the team's coach, has described her as a cunning individual, suggesting a sharp, tactical mind beneath her friendly exterior. She also demonstrates a high level of academic ability, having considered attending an elite school with a very high entrance difficulty, indicating she is a well-rounded and intelligent individual.

In the narrative, Ako serves as the team's lieutenant, playing in the second position of their matches. Her role is crucial as a steady and highly skilled competitor. Her mahjong style is defined by speed and efficiency rather than flashy supernatural abilities, which are common among other powerful players in the series. Her specialty is a quick, offensive style focused on completing hands rapidly. She excels at recognizing opportunities to call tiles to form open yaku such as sanshoku doujun or ikkitsuukan, allowing her to build winning hands faster than opponents who wait for more complex or expensive combinations. This gives her an excellent sense for the flow of the game and allows her to consistently gain points. Despite lacking a unique ability, a professional commentator notes that she may be the most fundamentally skilled player on the Achiga team, but her talents are often overshadowed by the extraordinary abilities of her upperclassmen.

Key relationships define her character arc. Her friendship with Shizuno is the emotional core of her return to Achiga, while her desire to reunite with Nodoka at the national tournament is her main driving force. She also shares a significant connection through her older sister, Nozomi Atarashi, who was a former teammate of coach Harue Akado during Achiga's golden era, linking Ako to the school's legacy. Over the course of the story, Ako shows development by integrating back into the team, using her solid middle-school experience to support her friends. While other players rely on unique powers, Ako's growth is showcased through her reliable, high-level fundamentals and her ability to analyze opponents and maintain composure under pressure, proving that skill and strategy are powerful forces in their own right.