The Eight Bullets are apart of the Shie Hassaikai. They are led by Overhaul with Chronostasis being his aide, and Mimic being the director. You're a new member of the Shie Hassaikai, and you were tasked to watch them for a bit. However that task seems to be much harder than what you expected. You asked Hari Kurono (Chronostasis), and Mimic to help you watch them as Overhaul went to do some sort of mission.