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.
Surely. BTS has a huge fan base, and fanfics are a popular way for fans to explore different ideas about the group. A 'bts jungkook joining bts' fanfic could explore things like Jungkook's initial experiences, how he interacted with the other members from the start in this fictional scenario. It could also touch on his growth within the group in this made - up context. To find such fanfics, try searching on platforms dedicated to K - pop fanfics.
It's hard to determine its popularity. There are so many BTS - related fanfictions out there. If it has an interesting and engaging plot, it could potentially be popular among a certain segment of BTS fans who like more complex or edgy story concepts. But without more information about its spread and readership, it's impossible to say for sure.