"Rape" doesn't enter into the equation of Christ's incarnation.
Mary wasn't violated.
Christ was formed strictly from her "seed",
her egg alone by the power of the Holy Ghost in whom she was enfolded.
God is indeed a king,
but He is the King of kings.
The kings are of fallen Man.
As the King,
God does not ask permission,
but what He never sins.
Rape is the purview of Man in his fallen nature,
not the nature of the Divine King.
However, though Jesus was indeed a Man,
He was also God the Word who came down from Heaven before His incarnation.
God doesn't sin,
which is why Jesus never sinned,
because He was (is) both fully God and fully man.