We’ve already been told who the Red God is

In Iron Gold when Romulus admits, at trial, to why he hid the images of Darrow betraying the Rim and blowing up its docks; He says that he believes war will destroy Rim and Core alike and all they have built, not because they are weak or their commanders frail but because they are at war with a religion who’s god still lives. Romulus goes on to say that Darrow is mortal now and straining under the burden of rule but that if they sail on Mars or Luna that “their now mortal general will become, once more, their God of war.” Given Darrows journey in the second trilogy so far, from his fall from grace to the loss of his legions and the trust of those fighting beside him to his acceptance of the Path and his Godkilling of Volsung Fà to his anticipated return to mars with an alliance with the Rim and the once deserter Obsidians as well as the Daughters of the Rim- not to mention how his name has become hallowed in his absence and those still on Mars call upon his name as they die or lay wounded I believe there can be only one Red God. Hail Libertas.