Other ninja from different villages would be quite curious. They might not understand the relationship between Gaara and Naruto at first. Some might see it as a weakness in Naruto, that he needs someone to protect him so much. But as they get to know more, they could come to respect the bond. For example, Neji might initially be skeptical, but after seeing how it actually helps Naruto in some ways, he could change his view. And characters like Shikamaru would just find the whole situation a bit of a headache, as it adds another layer of complexity to the group dynamics.
Sakura might be a bit annoyed at first. She's used to Naruto being independent and always charging forward, and Gaara's overprotectiveness could seem like it's getting in the way. Kakashi, on the other hand, would probably be more understanding. He'd see the value in Naruto having someone looking out for him, but he might also try to encourage Gaara to let Naruto grow on his own a bit. Sasuke could have a very negative reaction. He might see it as Gaara trying to steal Naruto away from him in a sense, especially if he has his own unresolved feelings towards Naruto.
Well, it could change the storyline in many ways. For one, Naruto would have an even stronger support system. Gaara, being overprotective, might prevent Naruto from getting into some of the more dangerous situations he usually jumps into. This could potentially slow down Naruto's growth in terms of combat experience as he'd be shielded from some threats. But on the other hand, it could also give Naruto more emotional stability, which could in turn help him better control his chakra and learn new jutsus faster. Gaara's presence as an overprotective brother could also affect how the other characters interact with Naruto. Some might be more cautious around him because they know Gaara is watching over him like a hawk.
Hinata would be heartbroken. She loves Naruto deeply. Her world would shatter. She might try to find out the truth behind his death, not believing that his friends could do such a thing without a good reason. And she would probably hold a grudge against those involved.
He might start to compare the fanfiction world too much with the real Naruto story, which could lead to some confusion. For example, if a fanfiction has a completely different view of a character's personality, he may struggle to separate it from the original.
For the other shinobi in the Hidden Leaf Village, Gaara's protectiveness towards Naruto could change their perception of Gaara. They might start to trust him more and see him as an ally rather than just a former enemy. This could lead to more cooperation between the Sand Village and the Leaf Village. For the younger generation of shinobi, like Boruto and his friends, they could look up to Gaara as an example of loyalty and brotherhood. Gaara's actions towards Naruto could inspire them to be more protective of their own friends and comrades.
Many characters would have interesting reactions. Tsunade would likely see it as an opportunity for Naruto to grow and diversify his skills. She might allocate some resources for his sword training. Jiraiya, if he were still alive, would probably be proud and see it as another step in Naruto's journey to become a great ninja. Gaara might view it as a sign of Naruto's ever - expanding power and be even more determined to keep up with him in terms of strength. And the Akatsuki members, if they knew, would probably start to re - evaluate Naruto as a more serious threat now that he has a new and dangerous weapon at his disposal.
Sakura might be really shocked. She always saw Naruto as a friend and a fellow ninja, and this would be a completely unexpected development. She might be a bit confused about how this would change their relationships. Sasuke, on the other hand, might be more indifferent on the surface but secretly curious. Kakashi would probably be very concerned. He's always been like a mentor to Naruto, and this situation would raise a lot of questions for him about Naruto's future and how this would affect the village. And the elders of the village would likely be in an uproar. They are always worried about the stability of the village, and this would be a huge bombshell that could disrupt the village's order.
Sasuke would likely be enraged. He and Naruto had a complex relationship, and Naruto was like a brother to him. He would probably seek revenge on Sakura immediately. Kakashi, as their teacher, would be deeply shocked and disappointed. He might struggle to understand how Sakura could do such a thing. The villagers would also be in turmoil. Naruto was their hero, and his death at Sakura's hands would cause a great deal of confusion and anger among them.
Hermione would probably be shocked at first. But then she would try to find a way to help Harry through it, using her vast knowledge of magic to figure out what's going on.
One possible storyline could be that they discover they are brothers early on. They then train together, combining Naruto's energetic and positive attitude with Gaara's more reserved and powerful sand abilities. They might face challenges from the ninja world together, like fighting against a new and powerful enemy that threatens the peace of all the villages.
The other characters' reactions would vary. Hinata could be happy for Naruto, even if it's not her he's proposing to. She has always respected Naruto's choices. Kiba might make some teasing remarks, like joking about how Naruto finally settled on Ino instead of chasing after Sakura all the time. And Choji would likely be supportive, since he's friends with both Ino and Naruto. He might offer to help with the wedding preparations if things go that far.