Regular Naruto and Sakura fanfictions usually focus on their positive aspects like friendship, love, and their growth as ninjas. But 'dark' ones might explore more negative emotions, darker storylines. And as for 'lemon', it's inappropriate content which regular ones don't have.
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.
In some fanfictions, Naruto might move on from Sakura by focusing on his ninja duties. He throws himself into more difficult missions, realizing that his life has a greater purpose than just pining over Sakura. This way, he gradually distances himself from his old feelings as he becomes more dedicated to protecting the village.
Yes, it can be a somewhat popular trope in the Naruto fanfiction world. Some fans like to explore alternative relationship dynamics. They might be interested in seeing how Naruto's relationship with Sakura could develop in a scenario where he 'steals' her from Sasuke. It adds an element of drama and can lead to interesting character development as Naruto might have to overcome his own feelings, Sakura's prior attachment to Sasuke, and Sasuke's reaction if such a thing were to hypothetically happen.
Well, in the original, Naruto has a more light - hearted and positive pursuit of Sakura. But in the case of Dark Naruto, it would be more complex. His darker nature might make Sakura more hesitant at first. So their relationship would develop more slowly, with more internal struggles for Sakura as she tries to balance her feelings with her perception of his darker side.
Maybe Naruto travels the world to learn new ninja techniques. Along the way, he meets new people and forms new bonds, leaving his feelings for Sakura behind. Another plotline could be that he devotes himself to rebuilding the Hidden Leaf Village and his love life takes a backseat.
One consequence could be that Sakura might feel neglected or confused. If Naruto has always been a part of her life and suddenly stays away, it would definitely have an impact on her emotions. She might start to question what she did wrong or if Naruto has changed in some way.