Tokyo Butei High School is a special institution that trains detectives who use force, commonly known as 'Butei.' Akari Mamiya, who has become a battle sister with the S-rank Butei Aria, faces a dire situation when her younger sister Nonoka is nearly poisoned by the oleander of Lee Woo, who once attacked their hometown. In exchange for the antidote, Akari is willing to sacrifice herself, prompting Aria to issue her first official operation order as a battle sister. The operation's code name is 'AA'! Now, with their respective feelings in their hearts, Aria and Akari fight to apprehend their greatest enemy yet. This is the third installment of a mid-scale action and daily comedy, featuring the cute and unique classmates of Butei High!