Masamune Mochizuki is the chairman of Mochizuki General Hospital and the founder of the Black Label vigilante organization. At 56 years old and standing 180 centimeters tall, he is a senior figure with grey hair and grey eyes. He is the father of Ryu Mochizuki, who was the best friend of the protagonist Arashi Mikami. After a terrorist attack left Arashi severely injured and Ryu brain dead, Masamune made the difficult decision to transplant his own son’s organs into Arashi to save his life. This event deeply shapes his role in the story. As the leader of Black Label, Masamune directs a team of select hospital staff and local teenagers in carrying out extrajudicial killings of individuals deemed cancers of society. His motivations are rooted in a personal tragedy: the death of his younger sister, whom he was unable to protect. This loss drives his obsessive desire to prevent others from suffering similar fates, leading him to establish the organization and dedicate himself to its cause. Masamune is a master strategist and manipulator, using his intelligence and authority to orchestrate operations and maintain control. He is assertive, confident, and uncompromising in his pursuit of justice, yet he operates by his own strict moral code. Throughout the series, he serves as a guiding and sometimes morally ambiguous force, pushing his agents to excise evil while grappling with the consequences of his past decisions.