There probably is. Fanfiction writers like to take existing characters and create different storylines. But it's important to note that this isn't part of the official Naruto story. In the original, Sasuke and Sakura are a couple, and Karin has her own relationship with Sasuke which is more of comradeship in the official plot. Fanfiction just gives people the freedom to deviate from the original.
One common theme is the exploration of unrequited love. Sakura's love for Sasuke is well - known, and when he leaves her for Karin, it delves into the pain of unrequited love from Sakura's perspective. Another theme is the idea of choosing based on power and usefulness. As Karin has certain powers that can be of help to Sasuke, it shows a theme of practicality in relationships.
Well, it could be a story about their complex relationships. Maybe it shows how they interact in a post - war Naruto world. Sasuke might be in the middle of Sakura's love and Karin's lingering feelings for him.
It changes the relationship between Sasuke and Sakura significantly. Instead of the canonical relationship where they end up together, Sakura is left heartbroken. This could also lead to a change in Sakura's character, perhaps making her more independent. As for Sasuke and Karin, their relationship becomes more central and they might face different challenges together as a couple.
There could be. Fanfiction writers sometimes come up with very creative and sometimes controversial ideas. However, this particular plot would be quite a deviation from the original story's themes of loyalty and friendship. In the original, Sasuke has his own complex relationships that don't involve such unfaithful behavior in this way.
There are fanfics like that. Sasuke might leave Sakura for Karin because of Karin's loyalty. Karin has shown unwavering loyalty to Sasuke throughout the series. She was willing to risk her life for him on multiple occasions. In contrast, Sasuke might think that Sakura's love is more of a childhood crush that she hasn't fully grown out of, and he may be drawn to Karin's more mature and selfless loyalty.
In proper fanfics rather than 'lemon' ones (as 'lemon' implies inappropriate content), Naruto is known for his never - give - up attitude. He's the heart of the story, always trying to bring Sasuke back and protect his friends. Sasuke is a complex character, with his family's past haunting him, which makes him seek power and revenge at times. Sakura, she starts as a girl with a crush but evolves into a capable ninja. These characteristics are often the foundation for fanfic authors to create interesting stories that don't involve improper content.
I'm not entirely sure if it's a 'popular' trope. Some fans might be interested in exploring such dramatic and controversial storylines in fanfiction for the shock value or to explore different character dynamics. However, many fans of the original Naruto series who ship Sasuke and Sakura would likely be disappointed or even offended by such a concept.
Sakura might be heartbroken. She's been in love with Sasuke for so long. She could initially go into denial, thinking it's just a temporary thing. Then she might get angry and vow to prove herself to Sasuke, perhaps by becoming an even stronger ninja.
One possible reason could be that Karin has unique abilities that are more useful to Sasuke in his goals. For example, her sensing abilities might be crucial in his missions. Also, Karin has a deep loyalty towards Sasuke which he might value more than Sakura's feelings at that time.