For Sakura, she could develop by learning from Itachi's sharingan abilities. Maybe she figures out a way to incorporate some of the perception and prediction aspects into her own fighting style. This would make her a more versatile fighter in battles.
Sakura could be developed in a unique way by making her chibi self more assertive in a different way. Instead of just being focused on Sasuke, she could be leading the way in adventures, using her intelligence and quick thinking. This would show a new side of her character.
A unique way to develop their relationship could be through a time - travel plot. They could be sent back in time to when they were children. This would give them the chance to change some of the events that led to their strained relationship in the original timeline. They could also get to know each other all over again, but with the knowledge and experiences they have from the future, which would lead to a very different and more intimate relationship.
One way to develop Naruto's character uniquely is to put him in a situation where he has to protect both Mikoto and Kushina at the same time. This would force him to use his skills in new and creative ways. He might also have to make difficult decisions between protecting them and fulfilling his duties as a ninja. For Kushina, her character could be developed by showing her interacting with the other villagers after being resurrected. She was a strong - willed woman, and seeing how she copes with the changes in the village could be interesting. Mikoto could be developed by having her mentor Naruto in some Uchiha - specific skills, which in turn helps Naruto understand the Uchiha better and also strengthens their bond.
For Sakura, her character can be developed by showing her growth in the Anbu environment. She could start off as a bit naive in some ways but gradually become more hardened and street - smart. For example, she might learn how to quickly assess threats from Itachi. Itachi's character could be developed by exploring his internal conflicts. Maybe in the fanfiction, he has to choose between his loyalty to the Anbu and his own moral compass when a certain situation arises. Sakura's presence could influence his decisions.
They could start by having more in - depth conversations. For example, Naruto could share his dreams for a more peaceful ninja world with Sakura, and Sakura could talk about her hopes for the growth of Konoha's medical facilities. This would deepen their understanding of each other.
To develop Roseline uniquely, you could give her an unusual hobby like collecting antique keys. This hobby could tie into the story in some way, like leading to a mystery she and Bella have to solve. For Bella, you could make her really good at parkour, which gives her a different kind of physicality and confidence. When they face challenges, their skills can play important roles.
For Hermione, you could develop her character by having her be more conflicted about the use of magic. Meeting Gellert, who has such extreme views on magic and power, could make her question her own Hogwarts - taught values. For Gellert, instead of just being the 'evil' character, show his more human side. Maybe he has regrets deep down. For example, Hermione could find a way to communicate with his past self and see his early dreams that were not so dark.
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.
They could develop a mentor - mentee relationship. Itachi uses his knowledge of the Sharingan to teach Naruto new combat techniques. As they train together, they bond over their shared experiences of loss and their desire to protect the people they care about. Naruto might also help Itachi come to terms with his past actions and find some peace within himself.
Their relationship could be developed through a series of flashbacks. For instance, Itachi could recall moments from Naruto's childhood that he observed while in the ANBU. These memories could make him see Naruto in a new light. Meanwhile, Naruto could learn about Itachi's past and the sacrifices he made. This exchange of knowledge could build a bond between them based on empathy and respect. In addition, they could train together in secret, with Itachi teaching Naruto some of his ANBU skills, which would also strengthen their relationship.