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.
A young girl idolizes the world-renowned S-ranked butei Kanzaki H. Aria and plans to follow in her footsteps; however, her test grades turn out as only an E-rank! All is not lost, however, as Aria agrees to give her some pointers. Can Aria help this newcomer become a first-rate butei?