In some cases, Karin can be more popular. Her backstory of being associated with Orochimaru and her survival instincts make her an appealing character. Some fans might be drawn to the idea of her as an underdog in the love triangle with Sasuke and Sakura. Also, her sensing abilities and her role in certain plot points in the original series can be explored more deeply in fanfics, which might make her more interesting to some readers than Sakura.
Another plot could be set in a post - war world. Sakura has built a life for herself as a respected medical ninja, but when Karin shows up, claiming that Sasuke still has feelings for her, a new conflict arises. Sakura decides to prove Karin wrong by showing how much she has grown and how well she can take care of Sasuke. Karin then challenges Sakura to various tests of strength and loyalty, leading to a series of events that put their relationship to the test.
Power struggles are also quite common. If they have different abilities or powers in the source material, the fanfiction might explore who is stronger, how they use their powers against each other, and what they can learn from their battles. It could also be about proving one's worth, especially in a world where power and status matter a great deal.
A common theme is competition. Since they are both characters with their own strengths, fanfictions often center around them competing for things like recognition, a certain goal, or the attention of other characters.
Often, Sakura is depicted as kind - hearted. She is the one who is more likely to see the good in people. Karin, on the other hand, might be more headstrong. For example, when they face a difficult situation, Sakura will try to find a peaceful solution first, while Karin is ready to jump into action right away.
I'm not sure specifically as it depends on the particular fanfic. It could be about a situation where Karin is shown bullying Sakura within the context of the fan - created story.
Maybe Karin has some personal reasons. For example, she might not like Sakura's character in the original work, so she also dislikes fanfic related to Sakura.
Well, Archive of Our Own (AO3) is also a great source. You can search for 'sakura vs karin' there. You may find stories where their abilities are pitted against each other, or perhaps fictions that delve into their backstories and how that affects their relationship in a competitive sense. It really depends on what kind of story you're interested in.
One popular theme is friendship. Writers often explore how Karin and Sakura form a strong bond, perhaps through shared experiences like training together. Another theme could be rivalry, where they compete in things like medical ninjutsu skills. And there's also the theme of self - discovery, as they both grow and learn more about themselves in the context of their relationship.
Well, Karin is for sure a main character as she is taking over Sakura's position. Sakura, although being replaced, still has an important role as the benchmark for Karin's replacement. Then, other characters in their shared universe who interact with either of them could be main characters too. For instance, Naruto could be involved, seeing as he is friends with Sakura and may have some sort of reaction to Karin replacing her. Also, characters from their respective teams or groups might be main characters as they would be affected by this replacement.
It could also be a misunderstanding. Perhaps Karin is misjudged by Sakura in the fanfic. Maybe Karin did something that was misinterpreted as malicious towards Sakura or someone she cares about, leading to the hatred.