A princess of the North, come to offer herself as a sacrifice to the demon king-
Except “she” is really the hero, come to defeat the demon king.
“So it’s true that the demon race can’t tell the difference between male and female humans.”
With those words, the hero plunges a silver dagger into the demon king’s weak point, his heart…only to find out that there was a flaw in his intel, and that the demon race isn’t blind to the difference in human sexes, but that they just have no need of differentiating.
Now the hero has fallen into the demon king’s clutches as his woman, and his body is slowly starting to change into a lustful one that takes pleasure in having semen fill him up-