The 7th Serious Crime Team is located on the seventh floor of the East Building of S City Police Station, with the rooftop above and the archives below. It's usually quiet and eerie here, with few people coming. All employees wear plain clothes and rarely show up. In S City, which has a very good public security, the 7th Serious Crime Unit is like useless. Every time the police department cuts expenses, the question of whether the 7th Serious Crime Unit should be retained is the subject of debate. This is where my story begins.