The S-Models have been recently discovered to be almost like a robot (secret) police. Robot S13 in fact was an S-Model who became a "heretic" and went into hiding due to his prophecies of the coming of "the Angel" (now thought to be Kat). In Chapter 41: Changes, the S-Models discovered the whereabouts of Robot, took him to a secret headquarters/interrogation room and only changed their minds about destroying him when they verified Kat's abilities as truly "Angelic" and bestowed upon her the symbol of their creator, Diego.