Eye of the North Wind — B.Y. Yan

Deep in the dunes a crippled son has come on the advice of his renowned father to earn into the illustrious Hundreds of the Wasteland King, before being robbed by an unhappy misunderstanding.  But where a door closes a literal window of opportunity opens, and he soon finds himself accompanying his master in search of a missing army.   
The young monarch, however, knows nothing of his presence or contributions. And for the sake of his pride he must never learn he has a secret protector -- even when contending with the indomitable courage of harlots, laying claim to the wealth of Creatures of Calamity, or facing down the wrath of Dead Gods. 

That is, unless the Greatest Standard Bearer to ever stand at the king's side chooses to come clean to uphold his promise at the cost of everything he has achieved in a world of scrap, fire, and iron.