Another plotline might be exploring Naruto's past more deeply. Maybe there are secrets about his parents that were never fully revealed in the original. In the fanfiction, he could discover something new about his father's time as Hokage or his mother's Uzumaki heritage that changes his perspective on his own powers and responsibilities.
It is generally considered unethical. Teenagers are not fully mature physically, mentally, or emotionally to handle the responsibilities of fatherhood. And older women in such situations may be taking advantage of the naivete of the teenagers. There are also legal implications in many places as having sexual relations with a minor is illegal, regardless of the resulting pregnancy.
In fanfiction, an older Naruto may have a more refined sense of leadership. He has seen more, experienced more battles and political situations. So, he might be more diplomatic in his approach compared to his younger self.
There are numerous social consequences. Firstly, it can lead to ostracism for both parties in many conservative communities. Secondly, it can cause a lot of family turmoil. The teenage guy's family may be shocked and struggle to accept the situation, and the older woman's family may also face embarrassment. Also, it can set a bad example for other young people in the community.
One common theme is the passing of the torch. Older Naruto is often shown mentoring the younger generation, like how Kakashi mentored him. Another theme is dealing with the scars of past battles, both physical and mental.
Older Naruto fanfic often has a different take on the characters. They might explore the backstories more deeply, like delving into Naruto's lonely childhood in ways the original didn't fully expand on. Also, they could introduce unique plot twists. For example, some might change the way the Chunin Exams happen.
Older Naruto fanfiction often has a more nostalgic feel. It was written when the Naruto series was still fresh in people's minds, so the authors were really exploring the initial concepts and characters. Many of them focus on filling in the gaps in the original story, like Naruto's early years or what happened between certain arcs. They also tend to be more influenced by the early art style and themes of the anime.
In such fanfictions, the plot might revolve around them teaming up for a mission. Maybe it's a mission that requires Naruto's brute strength and Hanabi's precision and knowledge of the Hyuga techniques. This could lead to them growing closer as they face challenges together. Their interactions during the mission, like Naruto making Hanabi laugh with his silly antics or Hanabi impressing Naruto with her skills, would be interesting to explore.
In many Naruto Shippuden fanfictions where Naruto gets sick, it often shows a different side of his character. Usually, his friends like Sakura and Kakashi would be very worried. Sakura might use her medical skills to take care of him. And his enemies might take this opportunity to try and attack. But Naruto's strong will would still be there even when he's sick. He might not be able to fight as powerfully, but his determination to protect the village would remain unshaken. This kind of fanfiction can explore the relationships in the Naruto universe more deeply when the main character is in a vulnerable state.
One possible fanfiction could be that Naruto is on a mission and encounters a powerful Uchiha who, instead of killing him, transfers his Sharingan to Naruto for some mysterious reason. Naruto then has to learn to control this new power while still maintaining his own unique ninja style.