He would be filled with a deep sense of grief. Naruto has always cared about Hinata, and her death would be like a part of him has been ripped away. He might isolate himself for a while, blaming himself for not being able to protect her. But eventually, he would use his pain as motivation to get stronger and fight against whatever caused her death.
One possible plot reason could be for Naruto to experience a great loss that changes his character completely. Maybe it's part of a dark plot where the enemy is so powerful that they manage to kill Hinata right in front of Naruto. This would fuel his rage and determination to become even stronger and seek revenge. Another reason could be related to some sort of sacrifice. Hinata might sacrifice herself to save Naruto or someone else important, and Naruto has to deal with the guilt and grief of her death.
Well, in such a fanfic, Naruto seeing Hinata in heaven could be a really emotional moment. It might start with Naruto being confused about where he is and then suddenly spotting Hinata. Their encounter could lead to a heart - to - heart conversation. Maybe they would talk about their past, their dreams, and how they felt about each other all along. It's a great concept for a fanfic as it gives an opportunity to expand on their relationship in a more spiritual and emotional setting.
She might immediately go to comfort him. Hinata has always cared deeply for Naruto, so seeing him cry would likely trigger her protective and empathetic side.
He would be filled with rage. Naruto has a strong sense of justice and the fact that someone took Hinata away from him would fuel his anger. He would vow to find and punish whoever was responsible. He might even become reckless in his pursuit of vengeance, endangering himself and those around him. His friends would have to step in to try and bring him back to his senses.
Well, in some fanfictions, when Naruto sees Hinata in the waterfall setting, it could be a moment of sudden realization. He might finally notice her in a new light, perhaps seeing her beauty and the depth of her feelings for him more clearly. It could be a turning point where he starts to develop deeper romantic feelings for her.
One possible plot could be that Hinata accidentally stumbles upon Naruto's memories during a mission. Maybe they are in a strange place where memories are made visible, and Hinata starts to understand Naruto on a much deeper level. She sees his lonely childhood, his determination to be recognized, and his dreams for the future. This newfound understanding could strengthen their relationship and make Hinata more determined to support Naruto in his goals.
One possible storyline could be in a dark AU (Alternate Universe). Maybe there's a powerful new enemy that targets Hinata specifically because of her connection to Naruto. This enemy could have some sort of vendetta against the Hyuga clan and sees Hinata as the key to their downfall. Naruto is then left to deal with the grief and also find a way to avenge her death, which could lead to a whole new arc of him exploring darker powers or making some difficult moral choices.
Well, in this fanfiction, an ending might be that Hinata, in her grief, leaves the village for a while to find herself. When she returns, she has become stronger and more confident. She then devotes her life to making the village a better place, just as Naruto would have wanted. Another ending could be that the whole village unites even more tightly after Naruto's death, with Hinata at the forefront of this unity, as she was the last person Naruto protected.
A common scenario in such fanfictions is that Hinata sacrifices herself in a war - torn situation. For instance, in a great ninja war, Naruto is the key to victory but is targeted by the enemy's most powerful forces. Hinata, with her unwavering love for Naruto, jumps in front of a massive attack aimed at Naruto, knowing full well that it will cost her life. This selfless act then serves as a major turning point in the story, inspiring Naruto and his comrades to fight even harder.