Even if Kiel accepts him, Why do you think he doesn't want Rood to know anything.Isn"t it bcz If Rood becomes the Demon King, He'll have to return to the demon realm?! Wouldn't that make Kiel lonely?! Kiel is being selfish by wanting to have Rood stay with him even though he know who Rood is but thats what any Human will do, right?