In the world of Hidan no Aria AA, there are special students called Butei who are authorized to carry weapons, investigate crimes and solve various incidents. One of the best of these students is an S-rank second year at Tokyo Butei High School named Aria Kanzaki. On the opposite end of the scale is E-rank first year named Akari Mamiya.
Akari Mamiya is in Year 1 at Tokyo Butei High School. Although she is currently in E Rank, her goal is to become a BUTEI like Aria Kanzaki, an Upperclassman in Year 2. In order to receive training from Aria, Akari submits a request to become Aria’s Amica.
Since Akari has been talking about Aria all the time after she became Aria’s (yet to be official) Amica, Shino increasingly becomes worried that Akari may not stay a close friend with her. In order to resolve the situation, she invites Akari to her home.
Kirin Shima is a junior high school student and an intern at Butei High School. Last year, she was an Amica with Riko Mine (current Year 2 student); however, she’s determined to become Raika Hino’s Amica this year. Will Raika accept her request?
Quartet refers to an actual fighting test between two four-person groups and is a requirement for all the Year 1 students at Butei High. Akari forms a group with Shino, Raika and Kirin and trains to defeat their opponent, Urara Takachiho’s team.
The Quartet match between Team Mamiya and Team Takachiho has begun. While Akari and Shino go out to find their opponent’s eye flag, Raika and Kirin defend their eye flag from an attack by Hina Fuma, who seems to know where their eye flag is.
Although Raika doesn’t want to admit it, she seems to be worried about Kirin and Riko’s relationship. On the other hand, Kirin is worried about Raika and Akari’s relationship. In order to resolve the situation, Kirin takes action.
Takachiho decides to take action to make her fantasies about getting close to Akari a reality. But when Shino catches on, she challenges Takachiho to a duel.
After asserting that her love for Akari is stronger than Shino's, Urara Takachiho invites Akari on an exclusive visit to her family's water park, but others end up tagging along – including Shino.
Since there have been a series of attacks targeting BUTEI, Aria comes to stay with Akari and Nonoka for a while in case she’s being targeted by criminals who wish to retaliate against her. At the same time, Aria tries to see how Akari lives as well.
Aria is injured in a gun battle and taken to the hospital. Meanwhile, after Kyochikutou declares that no one will have to get hurt if Akari surrenders to her advances, Akari tries to send Nonoka to stay with their aunt in Nagano.
Akari decides to fight Kyochikutou together with her friends. Kyochikutou demands that Akari give her Takamakuri, one of the Mamiya techniques, and threatens to kill everyone if Akari doesn’t give her what she wants.
Kyochikutou’s sister, Suimitsutou, goes on a rampage while demanding to have her sister returned to her. Aria, Akari and the others work together to bring her down.
