His friends like Choji would be shocked and would immediately side with Naruto. They would see this as an unfair and cruel act by Kiba. Sasuke, if he were around, might have a more complex reaction. He might initially think Naruto is weak for getting into such a situation, but then his sense of rivalry and his underlying care for Naruto might make him take action against Kiba. Tsunade, as the Hokage, would surely not allow such a situation to persist in the village and would enforce the rules to protect Naruto's dignity.
Most of Naruto's friends would be outraged. Shikamaru, known for his intelligence, would likely come up with a plan to get Naruto out of this situation. Hinata would be very worried about Naruto and might even try to stand up to Kiba herself, despite her usually shy nature. The senseis in the village, like Iruka, would also not tolerate such behavior and would step in to put an end to it.
Well, in this kind of fanfiction scenario, it could start with Kiba having some strange motive. Maybe he wants to show dominance over Naruto for some reason. He could use his skills with his dog, Akamaru, to intimidate Naruto into this 'pet' role. Naruto, being Naruto, would probably resist at first but then find himself in a situation where he has no choice. For example, Kiba might blackmail him with some secret Naruto doesn't want revealed. And from there, the story could develop into a series of events where Naruto has to navigate this new and demeaning role while still trying to be true to himself and his friends.
Naruto would probably be shocked at first. He might not have expected Hinata to leave him for Kiba. He could be angry at himself for not noticing Hinata's unhappiness sooner.
Shikamaru would likely be the voice of reason. He would tell Naruto to think things through clearly and help him come up with strategies for dealing with the new situation. Choji might bring over some food to help Naruto out, as he knows how difficult it can be to take care of a child. Ino would be more interested in the child's appearance and would offer to help Naruto with things like shopping for the child's clothes.
Sakura would probably be very shocked and disappointed in Naruto. She has always had deep feelings for him. Kakashi might be more level - headed, trying to figure out how to handle the situation from a strategic and diplomatic point of view.
Naruto would probably be extremely confused at first. He has always seen Itachi as a complex figure, and suddenly being forced to marry him would be a huge shock. He might feel angry that he has no say in this. Itachi, on the other hand, would likely be stoic on the surface but internally be very conflicted. He has his own burdens and this unexpected situation would add to them.
Sakura would probably be the first to jump into action. As a medical ninja, she'd immediately start examining Naruto and try to figure out the cause of the fever. She might be worried but also very focused on treating him.
Naruto would be extremely hurt. He loves Hinata deeply and to find out she cheated with Kiba would be a huge blow to him. He might go into a state of shock and disbelief at first.
Shikamaru would likely be lazy about getting involved at first. But if it started to cause a big ruckus in the village or among their group of friends, he'd step in. He'd probably analyze the situation quickly and try to find a logical solution. He might tell Naruto to cool off and Kiba to stop provoking Naruto if that was the case.
Iruka would probably be one of the first to notice and try to step in. He has always been like a father figure to Naruto. He would likely confront Kushina and try to protect Naruto. Sasuke might be a bit more conflicted at first. He has his own issues, but seeing Naruto being abused, he would probably end up on Naruto's side and try to figure out what's wrong with Kushina.
Iruka would be inconsolable. He was like a father figure to Naruto in the early days. His death on his birthday would bring back all the memories of Naruto's growth and how far he had come. The village as a whole would go into mourning. Naruto was the hero who saved them multiple times. There would be a sense of hopelessness among the villagers, and they would struggle to find a new source of inspiration without Naruto around.