He might also be confused. Kiba knows Naruto as a friend, so seeing Naruto hold Akamaru hostage would be completely unexpected. He may try to talk to Naruto first, asking him what's going on and trying to reason with him, while also being on edge and ready to attack if necessary.
One possible motive could be that Naruto is being controlled by some dark force or genjutsu. Maybe an enemy has manipulated his mind to target Akamaru in order to get to Kiba. Another reason could be a misunderstanding. Naruto might think Akamaru has been infected with something dangerous and he's trying to keep it away from others by holding it hostage, but in a very wrong way.
One way is through shared adventures. For example, they could go on a mission together where they face a really tough enemy. This would make them rely on each other more and deepen their bond. Another way is if Naruto starts training Akamaru in some new skills. This would not only make Akamaru stronger but also show Naruto's care for him.
One possible fanfiction could be about Naruto and Hinata going on a mission with Akamaru. Maybe they encounter a powerful enemy and have to work together using their unique skills. Naruto with his shadow clones, Hinata with her Byakugan, and Akamaru with his enhanced senses. They could form an unbeatable team and learn more about each other in the process.
One possible fanfiction could be where Naruto discovers a dragon during one of his solo adventures. Maybe the dragon is injured and Naruto uses his kind heart and ninja skills to heal it. As he holds the dragon, he forms a special bond with it, and the dragon becomes his powerful ally in future battles against stronger foes.
Perhaps in the fanfiction, there's a new threat to the village that requires special skills to defeat. Naruto's rasengan, Hinata's gentle fist, and Akamaru's ability to transform into different forms could be combined in unique ways. They might have to train together to master these new combined techniques. For example, Hinata could use her Byakugan to find the weak points of the enemy, Naruto could attack with the rasengan guided by Hinata, and Akamaru could provide a distraction or additional support.
One interesting Naruto and Akamaru fanfiction could be about Akamaru getting lost in the forest during a mission and Naruto using his shadow clones to search for him. They might encounter some rare and dangerous beasts along the way, but Naruto's determination and Akamaru's loyalty would shine through in the end.
In this fanfiction, perhaps Akamaru's 'in heat' state causes some chaos in the village. Naruto then uses his ninja skills to keep Akamaru in check and prevent him from causing too much trouble. He might also seek advice from Kakashi or other experienced ninjas on how to deal with it.
First, know the characters well. Naruto is brave, determined and a bit of a goofball, while Akamaru is loyal and has a strong bond with Kiba. Then, come up with an interesting plot. It could be a new adventure they go on together, or a problem they have to solve. For example, a mystery in the Hidden Leaf Village that only they can solve.