Kairi could be looking for an opportunity to use her physical combat skills. If she can get close enough or find a moment of weakness in Young Xehanort's grip, she might try to land a blow or use a self - defense move to break free. She may have learned some basic combat moves from training with Sora and Riku, and she could be relying on those in this situation.
One possible reason could be that Young Xehanort is very powerful. His strength might be overwhelming for Kairi, both physically and in terms of his dark magic if he uses it against her. Another reason could be that Kairi is in an unfamiliar situation. Maybe she's in a strange place or time where she has no allies to help her, which makes it difficult for her to fight back against Young Xehanort's grip.
One possibility could be that young Xehanort grabs Kairi as part of a plan to manipulate Sora. He might think that by having Kairi in his control, he can draw Sora out and into a situation where he can be easily influenced or defeated. This could lead to a series of events where the heroes have to figure out how to rescue Kairi from Xehanort's clutches while also dealing with his larger scheme.
Aqua, if she were involved, would be determined to save Kairi. She has a strong sense of justice and protecting the innocent. She would likely use her magic to try and track Xehanort and Kairi. Donald and Goofy would be loyal to Sora and follow him into the fray, but also try to keep Sora from making hasty decisions. They would offer their support in combat and also try to think of practical ways to free Kairi, like finding Xehanort's weaknesses.
The plot might involve Sakura being held by Tomakazu in a way that restricts her freedom. She could be struggling because she has a different goal or belief. For example, if they are in a fictional world with different factions, and Tomakazu's grip represents his side's control, and Sakura is trying to get to her own side or do something that goes against what Tomakazu wants.
Obviously, Sakura and Tomakazu are the main characters. Sakura is the one who is struggling, so she's a central figure in the story. Tomakazu, on the other hand, is the one whose grip is causing the struggle.
It could be about Sakura being in a difficult situation while in Itachi's grip, perhaps in a battle scenario where Itachi has the upper hand physically. Maybe she's trying to break free to either save herself or someone else.
There could be many authors who might write such a fanfiction. It could be an amateur writer who is a big fan of the Naruto series and just wanted to explore this particular scenario between Sakura and Itachi.
The plot might center around Sakura's internal struggle while under Tomokazu's grip. For example, she could be fighting against his control on an emotional or mental level. It might also be part of a larger story where there are other characters and events that are affected by this situation between Sakura and Tomokazu. Say, there are friends of Sakura who are trying to rescue her from this situation.