The Silent Authority. This secret violent institution was created by the various countries and the Church. It was formed by elite musicians from every field to protect the stability of human society. It was organized by the three kings. They were protected by the countries and could go anywhere. They were basically a spy organization—and the most troublesome one at that.
They were responsible for maintaining the world's stability and peace, eradicate cults, capture dark musicians, and even arrest musicians who broke the rules. All registered musicians must cooperate with them fully when needed or even make sacrifices at times.
Most of the time, they would not appear in public for secrecy. Even in the Sacred City, they just rented a storefront and have three secretaries visible. Most members were secret and had double identities or more. People would not know their true roles until death.