Hinata would probably be angry too. She might be angry at the circumstances that led to Naruto's death, whether it was an enemy or some other misfortune. She could direct her anger towards training harder, vowing to become stronger so that she can prevent such a tragedy from happening to others in the future.
After crying, Hinata may try to preserve Naruto's memory. She could start initiatives in the village like building a memorial or starting a training program in Naruto's name. She would also be there for Naruto's friends, offering them comfort and support, while still dealing with her own pain on the inside. She might even write down all her memories of Naruto in a journal, as a way to keep him alive in her heart.
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.
Hinata would be in shock. She'd probably freeze for a moment, unable to believe what she's seeing. Her eyes would be wide open in horror.
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 could be that Naruto sacrifices himself in a great battle against an ultimate enemy. Hinata, who has deep love for Naruto, is devastated. She might cry inconsolably as she remembers all their moments together, from when she first noticed him as a child to their more recent interactions. She could also vow to carry on Naruto's legacy in the village, while mourning his loss privately.
He would feel a deep sense of guilt, thinking that if he had been stronger or more aware, he could have saved her. Naruto might also start to cherish the memories he had with Hinata more, and this could change his personality a bit, making him more somber at times. He would probably vow to protect the things that Hinata held dear, like her family and the village.
Hinata might be shocked at first. She has always adored Naruto, and this sudden act of aggression from him would leave her stunned and unable to process it immediately.
She would be devastated. Hinata has deep feelings for Naruto. His death would likely cause her to go into a state of shock and disbelief at first. She might blame herself for not being strong enough to protect him.
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.
Naruto, being the energetic and battle - loving guy he is, would likely be on the edge of his seat, eager to see who comes out on top in each death battle. He might be making bets with himself about the outcomes. Hinata, with her gentle nature, would be a bit more subdued. However, she would also be intrigued. She might be more concerned about the safety of the fighters, even though it's just a fanfiction battle. And when a fight gets really intense, she might clutch Naruto's arm without realizing it, while Naruto is too engrossed in the action to notice at first.
Hinata might be very hurt. She's a sensitive person, so Naruto yelling at her could make her feel small and sad. She might start to doubt herself and her abilities.