Well, it could also be a plot device to drive the story forward. The jewel could attract the attention of other characters, both good and bad. This would lead to various conflicts and adventures for Sakura. It might also be related to her family heritage in the fanfic world. Maybe it was passed down through generations and now she has to figure out its true purpose and how to use it to her advantage.
In many fanfics, such a jewel could be a magical or mystical element. It could be a source of her strength, like giving her the ability to perform special jutsu or have enhanced senses. It might also have a connection to her relationship with Sasuke. For example, it could be a gift from him in the past or something that binds them together in a special way.
It could be the key to solving a major mystery in the story.
If Sakura dies in a fanfic, it could have a huge impact on the whole Naruto -verse within that story. Her friends like Naruto would be deeply affected. Naruto might feel like he failed to protect her, just as he felt about other losses in his life. And for the medical ninja community in the fanfic, her death could be a big blow as she was a talented medic.
It might explore different aspects of Sasuke and Sakura's characters within the context of a fanfic. For example, it could show Sakura with different abilities or Sasuke having a different attitude towards her. Since it's a fanfic, the author has the freedom to deviate from the original storyline and create something new. It could also be about their relationship in a different time period or setting, like in a modern - day AU (alternate universe) or in a completely fictional world.
A fanfic could show Sakura sacrificing herself to save Sasuke. This would be a very emotional and heroic end for her. Sasuke would then have to live with the guilt and the memory of her selfless act.
Well, one possibility could be that it's a dark fanfic where an enemy of Sakura kidnaps her to get to Sasuke. Maybe they want to use her as bait to lure Sasuke into a trap. Since Sasusaku is a popular pairing, the kidnapper might think that Sasuke would do anything to save Sakura.
I'm not entirely sure as I haven't read this specific fanfic. But generally, in SasuSaku (Sasuke and Sakura from Naruto) fanfics, it could be about some new adventure that breaks Sakura's seal and how that impacts her relationship with Sasuke and the overall story world.
One popular sasusaku evil sakura fanfic might be 'The Darkened Sakura'. In this story, Sakura's character takes a dark turn perhaps due to some unforeseen circumstances in the Naruto universe. Another could be 'Evil Sakura's Ascent' which shows how Sakura uses her skills in a more malevolent way. There's also 'Sakura's Shadow Self' where an alternate, evil version of Sakura emerges and causes chaos in the village.
It could be Orochimaru. He's always been interested in Sasuke and might see kidnapping Sakura as a way to manipulate Sasuke. He could use Sakura as a guinea pig for his experiments or as a bargaining chip to get Sasuke to come to him.
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.
The significance could be about exploring the inner workings of a novel. It might refer to delving deep into the characters' minds, themes, and plot structures from within the story, like turning it inside out to see all its components clearly.