He might become very withdrawn. Bell could start to isolate himself from others, especially those associated with Hestia. He may no longer trust as easily as he did before.
Naruto would be extremely enraged. He would vow to rescue Sakura no matter what. He would immediately start gathering his friends and form a rescue team. Sasuke, on the other hand, might initially seem more reserved but would also be determined to get Sakura back. He would use his Sharingan skills to track Madara.
Harry would be on guard at first. He has faced many dark threats in his life, and Madara would seem like another one. But as he gets to know Madara better, he might see some similarities in their struggles. Dumbledore would likely be very interested in Madara. He would try to understand Madara's motives and see if he could be an ally or a threat to the wizarding world. Dumbledore would be cautious but also open - minded in dealing with this new and strange character.
The Leaf Village would be in chaos at first. Hinata is an important member of the Hyuga clan, and her kidnapping would not be taken lightly. The Hokage would immediately call for an emergency meeting. They would start by sending out search teams, likely led by some of their best shinobi like Kakashi or Shikamaru, who are known for their intelligence and combat skills.
The gods would have a variety of reactions. Some might see it as a sign of something special, perhaps a new era beginning. Others might be more cynical and think it will bring trouble. For example, Freya might be interested in the child's potential and keep a close eye on the family. Zeus, if he were still around, might offer his wisdom on raising a child with such unique parentage. And Hermes could spread the news far and wide among the gods and mortals alike.
Sasuke would be furious. He has a deep connection with Naruto, and he would immediately start looking for Naruto. He might go on a solo mission to find and rescue Naruto, using all his skills and powers. Sasuke would not rest until he got Naruto back safe.
Sakura would probably be shocked at first, but then she'd get angry. She'd immediately start to struggle and try to free herself. She might call out for help if she thinks there are allies nearby.
The other Konoha ninjas would be quite shocked. The Hokage, whoever it is at that time, would see Naruto's change as a potential threat to the village's stability. They would likely keep a close eye on him and try to figure out what caused this transformation. Meanwhile, the younger generation of ninjas who looked up to Naruto would be confused and disappointed. They expected Naruto to be their role model of a kind - hearted and positive ninja, not someone acting like the feared Madara.