In this fanfiction, Demon Naruto might have a different set of abilities. Hinata could be the only one who can calm him when his demonic rage takes over. The story could be about how they work together to save the Hidden Leaf from a new threat. Their relationship evolves as Naruto battles his inner demon and Hinata stands by his side, proving that their love can overcome any obstacle.
The plot could involve Naruto being turned into a demon through some dark magic. Hinata, being in love with Naruto, refuses to give up on him. She decides to train hard to be able to protect Naruto from those who want to destroy him. Along the way, they discover a way to reverse the demon transformation, but Naruto has to make a choice between his newfound power and becoming normal again.
One possible plot could be that Naruto, as the Demon King, has to protect Hinata from other dark forces in the ninja world. Since he has this new, powerful and perhaps feared identity, their relationship might face new challenges. People in the village could be suspicious of Naruto's new form and try to keep Hinata away from him.
One possible fanfiction idea could be that Hinata discovers Naruto has a half - demon side that he's been hiding. This could lead to a lot of interesting character development. Hinata, being the understanding person she is, might help Naruto come to terms with this part of himself. It could also introduce new powers and abilities for Naruto, and perhaps a new level of relationship between the two.
A cool plot could be that the entire village is under a dark spell, and only Hinata realizes that the demon king Naruto is the key to breaking it. So she embarks on a journey with him, facing various obstacles and enemies along the way, and during this journey, their relationship deepens.
One idea could be that Demon Naruto has to protect Hinata from dark forces in the ninja world. Since he has demon powers, he has unique abilities to fend off threats. Another could be that Hinata's gentle nature starts to tame the demon within Naruto, leading to a transformation in his power and personality. Maybe there could also be a plot where they go on a journey together to find a way to fully control Naruto's demon side without losing his humanity, and during this journey, they fall deeper in love as they face various challenges.
Perhaps a plot where an enemy targets Hinata to get to Naruto and the demon fox within him. Naruto then has to go on a journey to rescue her, all the while facing his inner demons, literally. Along the way, they could discover new things about their relationship and their own powers.
One interesting plot point is that the village elders are against Naruto and Hinata's relationship because of Naruto's half - demon nature. They fear that it will bring danger to the village. However, Naruto and Hinata are determined to stay together and prove that their love can overcome any prejudice. Also, Naruto's half - demon form could attract the attention of other powerful forces outside the village, either as a threat or as a potential ally, and they have to navigate these situations.
In this fanfiction, Naruto's development as a demon would mean he has to face the prejudices of the village all over again. This would make him more determined to prove himself. Hinata would develop her own skills in order to protect Naruto. She might also develop a new sense of leadership as she stands up for Naruto against the village's doubts. Naruto would learn the value of having someone like Hinata in his life and would strive to be a better version of himself, both as a demon and as a person who is part of the village.
A simple plot could be that Hinata gets injured while on a mission, and Naruto takes it upon himself to nurse her back to health. During this time, they have long conversations and get to know each other on a deeper level, leading to the start of their romantic relationship.
In some fanfictions, Demon Naruto's character may become more isolated at first. His demon nature makes him feel like an outcast, even from his friends. But Hinata's presence gradually changes him. She gives him the acceptance he needs, and this causes his character to soften. He starts to trust more and rely on her, which is a big change from his initial guarded state.
The plot could involve Naruto protecting Hinata from the Hyuga clan's strict traditions. Since he's not bound by those traditions as her brother, he could fight against the elders who want to keep Hinata in a subservient role.