One idea could be exploring the backstories of the rivals in more depth. For example, what made them become rivals in the first place. Maybe there was a misunderstanding in their past that led to their competitive relationship.
Since I don't know the details of 'divine rivals a novel', I can only make some general speculations. It could be that the story is set in a fictional world where there are different deities or divine - like beings. These beings might have different ideologies or goals, which lead to a rivalry. The plot might then revolve around how this rivalry affects the world they inhabit, the mortals in that world, and how the characters involved develop over time. There could be complex power dynamics, political intrigue, and moral dilemmas as the story unfolds.
First, you should really get to know the characters well. Read the original work again if you need to. Then, start with a simple concept, like a day in the life of the rivals. It can be a good way to ease into the story.
I haven't read the 'divine rivals novel' specifically, so I'm not sure about the exact main plot. But generally, it might involve conflicts between divine beings, perhaps a power struggle, or a story of love and betrayal in a divine realm.
Since I haven't read the 'divine rivals novel', I don't know the main characters. But usually, in such a novel, there would be at least two powerful divine beings as the main rivals.
The transition can be well - written by first building up the rivalry to a peak. Then, have a sudden event that makes them question their rivalry. For instance, they both get criticized by a professor unfairly, and they end up defending each other. This starts to break down the walls. After that, introduce shared interests outside of academics, such as a love for a particular type of music or art. As they explore these together, their relationship evolves. The use of internal monologues can also be great, where they each struggle with their new - found feelings for the other while still trying to hold on to their rivalry identity.
Sasuke could be a major rival. Since Sasuke also has strong fire - based abilities, he might see Naruto's growth as a Katon master as a challenge to his own skills. Another potential rival could be a new character introduced in the fanfiction, a prodigy from another village who is also focused on mastering Katon. There could also be older, more experienced ninja within the Leaf Village who might initially doubt Naruto's ability to be a true Katon master and thus become rivals in a sense as they test his skills.
There are quite a few potential rivals. For example, Paul could be one. He has his own unique battling style and might be intrigued by Ash's Alola - champion ways. Then there's Trip. He could see Ash as a target to boost his own reputation. And in Alola itself, some of the more ambitious students from the Pokémon school who are aiming to be the best might also become rivals, constantly challenging Ash to prove they are worthy.
There could also be a mysterious trainer who appears from time to time. This trainer has a very powerful and rare Pokemon that Troy is intrigued by. Their battles would be intense as Troy tries to figure out the mystery trainer's strategies.