In fanfiction, Naruto could be developed by having him face new moral dilemmas when interacting with Yubel. His character could grow by learning about different forms of power that Yubel represents.
Yubel could be developed by exploring her past through Naruto's influence. For example, Naruto's curious nature might make Yubel reflect on her own origin and she could change her view of the world. They could also have a power - sharing arc where they combine their abilities to become stronger, which would develop both characters in terms of power and relationship.
A possible fanfiction plot is that Naruto has a strange dream about a powerful being named Yubel. Intrigued, he sets out on a journey to find out more about her. Along the way, he meets different characters who either know about Yubel or have some connection to the power she wields. This journey changes Naruto in ways he didn't expect, and he eventually finds a way to communicate with Yubel across different dimensions.
For Naruto, you can focus on his growth in a different aspect. Since he already has his ninja skills, in a story with Aplessia, he could develop his emotional intelligence further. For example, learning how to better understand Aplessia's more complex and perhaps different emotional range compared to his friends in Konoha. For Aplessia, you can start by giving her a backstory. Maybe she has a troubled past that made her the way she is, and as she interacts with Naruto, she starts to open up and become more confident.
For Naruto, his growth could be shown in relation to Tigress's no - nonsense attitude. He might become more disciplined in his training. For example, he could learn to control his rasengan better by observing Tigress's precision in her attacks. His character could also become more introspective as he tries to understand Tigress's more reserved personality.
For Naruto, you could focus on his growth in a new environment. Since he's in a different world with Natsuhi, he might have to adapt his ninja skills. Maybe he starts to learn some new techniques from Natsuhi's world. For Natsuhi, you could show her becoming more confident. Naruto's presence and his can - do attitude might inspire her to be bolder. For example, if she was shy about using her powers before, she could start to use them more freely.
Towa could be developed by exploring her past. Maybe she has some traumas from her own world. Meeting Naruto and seeing his determination could inspire her to face her past. Also, her relationship with Naruto could soften her hard - edged personality as she becomes more involved with the kind - hearted people in the Naruto universe.
To develop Naruto's character in relation to Anko, he could be put in situations where he has to rely on her. This would make him realize that he doesn't always have to be the one in the lead. Anko could also introduce him to different parts of the ninja world that he hasn't explored yet. For Anko, Naruto could be the catalyst for her to change her somewhat aloof and solitary nature. His friendship could make her more sociable and collaborative, and she could start to see the value in teamwork, which is something Naruto highly values.
Naruto's character in Anbu could be developed by exploring his relationships with his Anbu teammates. He might learn new ways of thinking and fighting from them, and this could affect how he interacts with Ayame. Ayame, on the other hand, could be developed by having her face some sort of danger that forces her to become stronger. Naruto could then be the one to help her train and gain confidence. This would not only strengthen their relationship but also develop her character into a more independent and capable person.
For Naruto, he could develop by learning more about leadership from Tsunade. He already has his own unique style, but Tsunade's wisdom in leading the village could give him new insights. Sakura could develop her medical ninjutsu further under Tsunade's guidance and also become more confident in her combat abilities. Tsunade herself could develop by seeing the new generation, Naruto and Sakura, grow and be inspired to take on new challenges for the village.
For Naruto with Juubi powers, his character could be developed by showing how he struggles to control this new and immense power. In the context of Moka's world, he might become more cautious as he realizes the different nature of threats there. He could also develop new relationships with Moka's friends and enemies, which would shape his character further.
In a fanfiction, Dark Naruto could start as a completely unapproachable and angry character. Ino could start by simply observing him from afar. As the story progresses, she could gradually get closer, and through their conversations, Dark Naruto could start to open up. This would show his development from a closed - off, angry person to someone who is more trusting and Ino would also develop as she gains more courage to be around him.