For Boruto, he could develop from being a bit overconfident to a more mature and reliable ninja. Maybe through his interactions with Sumire, he learns to think more before acting. For Sumire, she could become more assertive. Working with Boruto, she might find the courage to voice her opinions more often and take on more leadership roles.
It could also be related to a prophecy or a pre - determined fate in the fanfic's plot. There might be some kind of dark prophecy that says Kawaki has to kill Naruto to prevent a greater evil. Or perhaps Kawaki is being controlled by an external force that has a vendetta against Naruto and uses Kawaki as a tool to carry out the murder.
One common theme is friendship. Writers often explore how Himawari and Kawaki, who come from different backgrounds, form a bond of friendship. Another theme is growth. They both grow as characters, learning from each other.
Kawaki makes his appearance in Boruto manga at a specific point, but I can't recall exactly. You might want to check the official manga sources for the precise chapter.
Well, perhaps in the fanfic, there could be a plot where Boruto gets injured during a battle and Sumire has to take care of him. While taking care of him, she discovers a side of Boruto that he usually doesn't show. And Boruto, in his vulnerable state, starts to see Sumire in a new light. This could lead to a budding romance between them.
Writers often portray Boruto and Sumire's love in fanfiction as a kind of young, innocent love. They might write about how Boruto makes Sumire blush with his cheeky comments, or how Sumire's presence makes Boruto more focused on his tasks. It's all about the small, cute interactions that show the start of their feelings for each other.
Their relationship could develop through shared experiences. For example, if they both get involved in a dangerous fight against a common enemy, they'll start to trust each other more.
One idea could be that they go on a secret mission together. During the mission, they face various challenges that test their skills and teamwork. This could lead to a deeper understanding and bond between them.