I don't think it's a common fanfiction plot. While there are all kinds of fanfiction out there, the idea of Pegasus's goons tying up Sakura is rather specific and not something you'd typically see in mainstream fanfiction. However, in certain sub - genres that deal with more action - oriented or darker themes, it might pop up, but it's not a widespread or common type of plot overall.
It could potentially mean that in a fanfiction story, the characters known as Pegasus's goons are physically restraining or incapacitating a character named Sakura. This might be part of a plot where Sakura is being captured or held against her will for some reason related to the Pegasus storyline in the fanfiction world.
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.