The game happens in the SCP Foundation Universe.
Going to the specifics, Jericho Squad is a Global Occult Coalition Strike Team sent to investigate the apparition of the City. Due to the extremely anomalous nature of the situation and the fact that Arnold Leach is a former agent, all members are Type Blues or Thaumatologists with different specializations except for Corporal Simone Cole,that is (unknowly to her) a Type Green that has not yet get into Phase Four. The reason she has not yet be executed as usual is because the G.O.C. scientists want to use her as guinea pig for the inclusion of Type Greens on the organization since they would be unvaliable allies agaist others of their Kind or event Type Blacks like The Firstborn.- Considering their religious nature, they're probably part of the Horizon Initiative rather than the GOC.
God didn't want to kill the First Born
If a small group of human sorcerers could kill the Firstborn, then logically [[God]] could. But He didn't. Sentimentality, part of the divine plan, or some other reason, the Gnostic text was wrong about why the Firstborn wasn't destroyed instead of Abandoned.