One common theme is family discovery. Since they aren't siblings in the original story, many fanfics explore how they come to realize they are related. Another theme could be protection. Naruto might feel the need to protect Karin as his sister, or vice versa.
Yes, there are some. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Naruto and Karin siblings' and you'll find various stories. Some might focus on their relationship development as siblings in different scenarios within the Naruto universe.
One idea could be exploring their family history. Maybe they discover they have a common ancestor who was a powerful ninja. This could lead to them uncovering hidden jutsu or secrets within their family lineage.
Naruto, having been banished, may initially lose his sense of purpose. However, with Karin by his side, he could find a new reason to strive. He might develop a more nuanced view of the ninja world and its politics. Karin, on the other hand, could develop a softer side. She has always been in a tough situation, but Naruto's kindness could make her more empathetic. She may also start to trust others more, especially Naruto, which is a big step for her character.
In this fanfiction scenario, their relationship would be deep - rooted in family love. Naruto would look up to Karin as an older sister, or if Karin was younger, he would be very protective. They would likely have a bond that goes beyond the typical shinobi comradeship. Karin could be the one to understand Naruto's loneliness as a child, and Naruto could be the one to bring out Karin's softer side. They might even develop a unique form of teamwork, combining Naruto's powerful jutsu with Karin's healing and sensing abilities for their adventures.
Naruto would likely develop more patience. He's used to being impulsive, but in an arranged marriage with Karin, he'd have to learn to be more patient and understanding. His view of relationships would also expand beyond his initial infatuation with Sakura. Karin would become less bitter. She's had a tough life, and being with Naruto, who has so much positive energy, would start to soften her. She might become more open - hearted and less focused on her past grudges.
In some fanfictions, the siblings could be entirely new characters created by the author. They might have unique ninja abilities like one sibling could be a master of wind and water jutsus combined. Another could be a prodigy in genjutsu, stronger than Sasuke in that aspect. And the third might be a non - combatant sibling who is more into the political and diplomatic side of the ninja world, helping Naruto in a different way than fighting.
The power dynamics between them are also interesting. Naruto has his powerful jutsu like the Rasengan and his Nine - Tails chakra, while Karin has her sensing abilities and medical knowledge. Fanfiction can play around with how they use their powers together in various situations, whether it's in a fight against a common enemy or in helping the village. Their combined skills could lead to unique plotlines and character developments.
Maybe she is a big fan of the Naruto series. Fanfictions often explore different aspects of the story and characters that the original might not fully cover. Karin could be attracted to the creative interpretations and new storylines in Naruto fanfiction.
A Naruto and Karin love story in fanfiction could develop in different ways. One possibility is that during their adventures together, they find common ground in their past traumas. Karin, having a difficult past, and Naruto, with his own struggles, could bond over that. They might support each other and eventually fall in love as they realize how much they mean to each other.