There could be many interesting fanfictions on this topic. One idea could be that in this fanfiction, the 'force' might be some sort of magical or emotional force that binds Harry and Ginny even closer during her pregnancy. It could explore how they deal with the impending arrival of their baby while also facing challenges related to this special force.
A plot could be that the 'force' is a mysterious energy that Ginny unknowingly absorbed. Now that she's pregnant, it's affecting her and the baby in strange ways. Harry has to research ancient texts and consult with wise wizards to find a way to control this force. Ginny, on the other hand, is dealing with the physical and emotional changes of pregnancy while also being a vessel for this unknown force. It could be a story full of mystery, adventure and family bonds.
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.
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.