Yes, it can be. In some horror literature, the idea of a demon and an act of violence like rape is used to create a sense of extreme horror and dread. It plays on the fear of the supernatural and the vulnerability of the victim, often a girl in such stories, to shock the readers.
One way could be to change the act of rape to a non - violent encounter. For example, the demon could be magically bound to the bedpost and the girl could be the one to free it through an act of kindness, turning it into a story of redemption instead of horror.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.
In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.
The main distinction of porn with a story genre from regular porn is the presence of a coherent narrative. Regular porn often jumps straight to the sexual action, while the story genre tries to add some kind of story framework around it. But in the end, both are adult-oriented and feature explicit sexual content.