It might be related to a connection with some powerful entity in the Wave arc. For example, if there's a secret shinobi from the past whose power is tied to the Rinnegan and Naruto somehow forms a bond with that power source, it could lead to the awakening. Also, the intense emotions and challenges he faces in the Wave arc might be a catalyst, pushing his chakra to a new level and awakening the Rinnegan.
It could be a water - based kekkei genkai. Since the Wave arc has a lot to do with water, it would make sense for Naruto to awaken a kekkei genkai related to water. This could give him an edge in battles, especially in the Wave region where water is abundant.
Naruto himself is often a popular character in such fanfictions. Writers might explore how his Uzumaki bloodline could be further developed or interact with other bloodlines. Sasuke is also a common choice. His Sharingan and potential new bloodline developments are always interesting to read about. Hinata is another one. Her Byakugan and the Hyuga bloodline can be the center of many fan - created storylines, especially when it comes to relationships and new abilities.
One implication is that he becomes much more powerful. The Rinnegan gives him access to powerful abilities like the Six Paths techniques, which would change the power dynamics in battles in the fanfiction. He could now face stronger enemies more easily.
Obviously Naruto is the main character. Sasuke is often involved as well. Since Naruto's new bloodline power can change the power dynamics in their relationship. Sakura might also be there, perhaps helping Naruto to control his new abilities. Kakashi could play a role too, guiding Naruto in understanding and using the power of his awakened bloodline.
One interesting concept could be the exploration of unique bloodline combinations. For example, a fanfiction might create a scenario where a character has a blend of two powerful bloodlines, like the Sharingan and the Byakugan, leading to entirely new abilities that we haven't seen in the original Naruto series. Another concept could be the origin of certain bloodlines, perhaps delving deeper into how they came to be in the Naruto universe's history. And also, the idea of bloodline mutations or evolutions within the fanfiction can be really engaging as it can introduce fresh and unexpected powers for the characters.
One possibility is that there's some ancient chakra or energy in Wave that interacts with Naruto's own chakra. The unique environment of Wave, with its water and nature elements, might have caused his Mokuton to awaken. Another reason could be that Naruto has some kind of connection to the First Hokage that gets revealed during the Wave mission, and that connection enables the Mokuton awakening.
One possible plot development is that Naruto's awakened bloodline gives him the power to manipulate elements in ways not seen before. For instance, he could combine fire and water to create a new type of steam - based attack. This new power would make him a target for powerful villains who want to either control him or eliminate him. As a result, Naruto has to go into hiding while he learns to master his new abilities, and he meets some interesting characters during this time who help him on his journey.
When Naruto awakens Mokuton in the Wave fanfiction, his role in the Wave mission is transformed. Mokuton is a powerful and versatile ability. Naruto could use it to camouflage the group by creating a forest - like environment, making it harder for the enemy to find them. He could also use wooden constructs to hold off attackers while the others carry out the main objective of the mission. This new power elevates his status from a novice ninja trying to prove himself to a crucial part of the mission's success.
Sasuke is often involved. Since he and Naruto have a complex relationship, Sasuke might react in various ways to Naruto's newfound power from the hidden bloodline. He could be jealous or see it as a new challenge to overcome in their rivalry.