well these guys are a blend after taking inspiration from batman, Iron man and moon night. These specters(agents) work for SPEC-OPS equip to handle any situations , they have a specter for any kind of Mission.
Here you can see SHADOW : Intel and assassination expert favorite weapon R.I.P 60 cal Sniper Rifle
and GRIM : well this guy likes get up close and personal equipped with reapers.(no matter how may times i redesign this guy he comes up looking like akuma)