The story of Season 23 begins when Ukyo receives an order from his superiors to compile the "150-year history of the Metropolitan Police Department". In the seventh year of the Meiji era, the Metropolitan Police Department was founded by the former Satsuma samurai, Kawaji Toshiyoshi. Together with the Secretary of the Interior, Okubo Toshimichi, he established the police organization and became the first Grand Superintendent (now the Metropolitan Police Commissioner). However, later on, Okubo suffered a tragic assassination. Just like the incident that happened at the dawn of the police, a big-name politician was killed! What stands in the way of the special mission unit that begins its investigation is the reality of the widening "rich-poor gap" in modern Japan, as well as the ambitions and conspiracies of the powerful people that are spreading in the political world! ? 150 years ago and now - as society changes, has "justice" also changed...! ?