Watch Aria the Scarlet Ammo AA Online

The story takes place in Tokyo Butei High School, a special school where armed detectives—"Butei"—are trained to use weapons. Kinji Tooyama is a second-year-student who has a special ability, but he keeps it a secret to maintain an ordinary, peaceful life; however, when he gets caught in a bombing on the way to school, he encounters H. Aria Kanzaki, the most powerful S-Rank Butei student in Assault Studies.

Akari Mamiya, a first-year student from Tokyo Butei High, idolizes the S-rank Butei Aria Holmes Kanzaki and wishes to follow in her footsteps. Despite only being an inept E-rank Butei, Akari's resolve to improve remains strong. After the idea of having an Amica contract (a senior-student mentorship program) with Aria is brought up, Akari submits a request form attempting to establish said contract. Her classmates and friends do not expect Aria to accept Akari's request, mainly because of the girl's strict selection process, but to everyone's surprise, Aria gives Akari a chance through a test, which Akari miraculously passes! However, Aria will not officially make Akari her Amica until Akari meets her standards. Training under Aria will be no easy feat, as she has to concurrently manage her relationships with her friends. Will Akari have what it takes to walk down the same path as her idol?

In response to the worsening crime rate, Japan creates Tokyo Butei High, an elite academy where "Butei" or armed detectives hone their deadly skills in hopes of becoming mercenary-like agents of justice. One particular Butei is Kinji Tooyama, an anti-social and curt sophomore dropout who was once a student of the combat-centric Assault Division. Kinji now lives a life of leisure studying logistics in order to cover up his powerful but embarrassing special ability. However, his peaceful days soon come to an end when he becomes the target of the infamous "Butei Killer," and runs into an emotional hurricane and outspoken prodigy of the highest rank, Aria Holmes Kanzaki, who saves Kinji's life and demands that he become her partner after seeing what he is truly capable of.