Plan-1055 Belial is an advanced Arm Slave (mecha) featured in the anime series Full Metal Panic!. Piloted by Leonard Testarossa, the Belial represents one of the most formidable threats faced by the protagonists. Unlike standard Arm Slaves, the Belial is equipped with cutting-edge technology, including the Lambda Driver, granting it overwhelming power and abilities. Its sleek design and exceptional combat capabilities make it a symbol of the antagonist's might. Belial plays a crucial role as the main adversarial machine in the series’ later arcs.