If we consider a more romantic relationship, it could develop slowly. Fuu could be the one to first show kindness to Dark Naruto when everyone else is afraid of him. This kindness would be a new experience for him, and he would start to open up to her. As time passes, their feelings for each other would grow deeper, and they would support each other through all the difficulties they face in the ninja world.
In the fanfiction, their relationship could develop in a very passionate way. Since Naruto is a very emotional and energetic character, and Fuu has her own charm. When they decide to have a child, they would be super excited about the future. However, they would also face difficulties like any couple. There might be times when Naruto's duties as a ninja conflict with his family life, and Fuu would have to be understanding. And vice versa. Through these ups and downs, their love for each other and their child would keep their relationship strong.
Before the marriage, Naruto might first develop a friendship with Fuu. She is a spunky and independent character. Then, as Naruto also gets to know Yugito better through joint missions and diplomatic encounters between their villages, he starts to feel a connection with her as well. Fuu and Yugito, initially a bit jealous of each other's closeness to Naruto, would eventually realize that they can all be happy together. They would then start to build a relationship based on mutual respect, love, and the shared goal of making the ninja world a better place.
Naruto would initially struggle with the formalities of a political marriage. But as he spends time with Fuu, he would start to adapt. His character would become more refined in terms of handling political matters. He would learn from Fuu's grace and intelligence. Fuu would also change. She might become more assertive, as she has Naruto by her side. She would be more involved in making decisions for the greater good of both villages. Their characters would grow together, with Naruto's boldness and Fuu's tact combining to create a strong leadership duo for their joined communities.
Naruto's personality would likely become more mature. The responsibility of being in an arranged marriage might make him think more about the future. He would still keep his positive and determined side, but now he has someone else to consider. Fuu's personality could soften. She might start to open up more and show her vulnerable side to Naruto. The marriage could be a catalyst for her to become more trusting and less guarded.
Their relationship could start off as antagonistic. Dark Naruto's actions might be seen as a threat by Anko, so she would be on the defensive. But as she gets to know him better, she might see the pain behind his dark transformation. This could lead to a more empathetic relationship where Anko tries to help Naruto come to terms with his new self.
Their love could develop slowly. At first, they might just be comrades. But as they spend more time together, they start to notice little things about each other. For example, Naruto might notice how Fuu's eyes light up when she's excited about something, and Fuu might notice Naruto's determination in tough situations. These small observations could lead to a deeper emotional connection over time.
Their relationship might start off rocky. Naruto's dark telepathy could make him seem more distant and brooding, which Ino might initially be put off by. But as she realizes he's in trouble, she'll try to break through to him. Eventually, they could develop a relationship based on mutual understanding and trust as Ino helps Naruto come to terms with his new powers.
It could develop gradually. At first, Dark Naruto might be hostile towards Ayame. But Ayame's kindness could start to break down his defenses. For example, if she offers him a place to stay when he's on the run. Then, they might start to have conversations where Ayame tries to understand his motives for turning dark. This could lead to a mutual respect, and eventually, love might bloom as they realize they have more in common than they thought.
If Naruto and Fuu had children in a fanfiction, their kids' abilities would develop in an interesting way. Naruto's natural talent for making friends and his strong chakra would influence them. They could easily make allies and have a large reserve of chakra. Fuu's stealth and her ability to adapt quickly would also be passed on. So, the children might be able to quickly learn new jutsu and use them effectively in combat situations. They'd grow up learning from two very different but powerful ninja, which would make their abilities diverse and formidable.
Their relationship could start with Naruko being curious about Dark Naruto. As she gets closer to him, she discovers his pain and the reasons behind his darkness. This understanding can lead to a friendship where she tries to help him. Eventually, it might develop into a deeper bond, like a romantic relationship if they share many experiences and grow to trust each other completely.