Omen might be Japanese, considering his link to Kingdom Corporation. Secondly, Omen and Yoru are the only two agents that feature teleportation abilities, as we know Yoru is Japanese, it might be that Japan does the R&D for teleportation technology and Omen was their 1st R&D subject due to which his identity is kept a secret.
Update : Based on Omen Lore, Omen is Oran McEneff abbreviated as Omen, who was a former employee/scientist for Kingdom Corporation. He was affected by the Radian Collider that we can find in the map Fracture, where we can also find the emails between him and Ruben that gave rise to this theory. Sabine AKA Viper, who is a chemist, is the person responsible for the survival of Omen.
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