The relationship could start with mistrust. For example, Selene might be seen as a threat by Naruto at first. But as they interact more, they could find common ground in their goals, like protecting the innocent. Their relationship might then develop into a friendship as they rely on each other in battles and share their life stories.
In a fanfiction, their relationship could be developed through shared hardships. Let's say they are both trying to stop an evil force. They have to trust each other completely during this mission. Naruto's positive attitude might start to rub off on Selene, who may be more reserved or jaded. And Selene's unique abilities can save Naruto in crucial moments. This back - and - forth of depending on and saving each other can lead to a strong relationship.
If Selene has some special knowledge or power, Naruto could be curious about her. He starts to ask her questions and they gradually become closer. They could also have some friendly competitions which help them understand each other better. As time goes on, they might develop a deep bond, where they are not just friends but also like family to each other in the fanfiction world.
Well, Naruto's Nine - Tails chakra is a huge power source. If he were to share some of that chakra with Selene, she could gain new abilities. Maybe she could use it to create a powerful shield around them, since the Nine - Tails' chakra is known for its raw power. On the other hand, Selene's power to control the blood of her enemies could be used to immobilize opponents while Naruto prepares his more complex jutsus. Their combined powers would be a very interesting and powerful mix that could be used to overcome many difficult challenges in the Underworld.
There could also be original characters created specifically for the fanfiction. These characters could be hybrids of the Naruto and Selene universes, perhaps having a mix of ninja abilities and Underworld powers. They could add new dimensions to the story and help drive the plot forward, whether as friends or foes to Naruto and Selene.
Some fanfictions could explore the idea of Selene teaching Naruto about the secrets of the Underworld. Naruto, in turn, could show Selene his ninja way and how determination and hard work can overcome great obstacles. This could lead to a series of adventures as they explore different regions of the Underworld together.
They could start training together more often. Through intense training sessions, they would grow closer as they learn from each other's strengths and weaknesses.
One plot idea could be that Selene, with her unique powers, somehow gets transported to the Naruto universe. She meets Naruto and initially they are at odds because of their different ways of handling things. But as they face a common enemy, they start to understand each other and work together. Their combined skills, Naruto's ninjutsu and Selene's otherworldly powers, make for an exciting adventure against the foe.
One possible plotline could be that Naruto, with his strong will and unique powers, somehow finds himself in the Underworld and meets Selene. They might initially be at odds as they come from very different worlds. Naruto could be intrigued by Selene's vampiric nature and her power over the night. They could form an unlikely alliance to face a common threat in the Underworld, like a powerful dark force that is threatening to disrupt the balance not only in the Underworld but also has implications for Naruto's own world.
The relationship can be developed through shared missions. When they are on a mission together, they can rely on each other's skills and learn from one another. For example, Naruto's vast combat experience can help Sarada in tough battles, and Sarada's fresh perspective can give Naruto new ideas.
In fanfiction, their relationship can be developed through shared experiences. For example, they could be trapped in a mysterious dimension together. During their time there, they have to rely on each other to survive, which makes them trust one another more.
Another way is through cultural exchanges. Naruto could introduce the Mizukage to some of the unique traditions of the Hidden Leaf, like the Ninja Academy system or the annual Chunin Exams. In return, the Mizukage could share the secrets of the Hidden Mist's special jutsu training. This mutual exchange of knowledge and experiences would bring them closer.
In fanfiction, a crisis situation can be used to develop their relationship. For instance, if the village is under attack and Shizune is in charge of treating the wounded. Naruto could be the one bringing in the injured. In this high - stress environment, they would see different sides of each other. Naruto might see Shizune's calm and efficient side in handling the chaos, and Shizune would see Naruto's selfless dedication to protecting the village. This would bring them closer together.