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.
Well, it could be that Young Xehanort captures Kairi to gain some kind of power. Since Kairi has her own unique abilities and significance in the Kingdom Hearts universe. He might think that by having her in his control, he can manipulate events to his advantage. For example, he could try to use her to access certain keyblade powers or to open paths to different worlds that are otherwise inaccessible.
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.
First of all, it's important to note that 'lemon' fanfiction often contains inappropriate content. However, in general, Momo might be depicted as having her own unique charm, perhaps being cute or having a certain innocence. Kairi, on the other hand, could be shown as strong - willed. But again, this is a very general view without referring to any inappropriate 'lemon' aspects.
Kairi might initially be in shock and fear. Being used as a human shield is a terrifying situation. She could freeze for a moment, not knowing what to do.
Perhaps in a fanfiction, Kairi somehow ends up in the Naruto universe. She is mistaken for a foreign ninja at first. Kairi tries to find a way back home while also getting involved in Naruto's adventures. She helps Naruto and his friends in some battles with her unique keyblade abilities. Along the way, Naruto and Kairi share stories of their respective worlds and form a deep bond.
Sora could be the one to save them. Since Kairi is important to Sora, he would sense that she is in danger. He would use his keyblade skills to fight off Gaston and free Kairi and Belle. Sora is known for his bravery and determination, and he would not let Gaston get away with such a malicious act.