Keiko Ichinomiya is a detective in the Tokyo Police Juvenile Department. She relentlessly pursues an investigation into a series of young men's deaths over six months, convinced they are homicides despite her superiors dismissing them as accidents and urging her to drop the case. This investigation fuels her persistent activities. Her personality blends ambition with a volatile temperament; frustration often erupts in shouts or strikes against nearby objects like furniture. To manage stress, she turns to video games, excelling particularly at beat 'em ups, and consumes alcohol, sometimes excessively. Her path crosses with the primary trio (Team AAA) during a competitive video game session at an arcade where she confronts Kazuo Saitō. This encounter leads her to confiscate a firearm from him, forging the investigative link connecting her to their involvement in the clandestine corporate competition.