The border cities and ports that separate the Yamato Republic from the Gray Zones typically consist of two parts - gang-controlled slums and the port control authority. Ever expanding criminal influence presents a great challenge to peace and stability, hence the Yamato authorities deploy the Kyoukai Shield Forces (KSF) to patrol the boundary zones between government and gang-controlled neighborhoods. Typically consisting of two to three KSF Sentinels led by a KSF Sergeant, KSF squads are armed with enough heavy gear to quell a formidable gang-backed insurrection. KSF are part of the warrior caste who enjoy considerable benefits as long as they remain in service and maintain an acceptable fitness score in the quarterly national health check. Those with high fitness scores, ample battle experience and the right connections are promoted to become sergeants, and may eventually qualify to join the prestigious samurai caste. Those who do not pass the health check are relegated to demotion or outright expulsion from the warrior caste.