Sasuke can also be involved. His intelligence in combat and his knowledge of various jutsu make him a great addition to a fanfic centered around intelligence. He and Naruto can have intellectual battles or work together to face a greater threat.
Tsunade could be part of it too. As the Hokage, she has a great deal of knowledge and strategic thinking. In a fanfic, she might mentor Naruto in using his intelligence in more political and leadership - related matters within the village.
Naruto himself is obviously a main character in such fanfictions. His growth in intelligence is usually the central focus. Sasuke can also be involved as Naruto's rival or ally in situations where intelligence plays a crucial role. Sakura, with her own intellectual capabilities in medical ninjutsu and general knowledge, often appears as well.
Obviously Naruto is often a main character in 'Naruto Crystal Fanfic' as it is related to the Naruto universe. Sasuke can also be involved, perhaps having a different view on the power of the crystal compared to Naruto.
Sasuke is often a main character in 'eye naruto fanfic'. Since he has the Sharingan, many fanfics explore different aspects of his eye power, like how he might develop it further or use it in new and unexpected ways. Another one is Hinata. With her Byakugan, fanfic writers can create stories about her using it in battles or for some other special purposes, like finding hidden secrets in the ninja world.
Naruto himself is often involved. Imagine a fanfic where Naruto finds a strange mask that gives him new powers, but also has some negative side - effects. Sasuke can also be a main character in such fanfics. He might be on a quest to find a mask that has a connection to his clan's history.
The Kazekage is the central figure in 'naruto kazekage fanfic'. But we also see characters like Sakura. She is a strong kunoichi and her medical skills could come in handy in a story set in the Naruto world. Another character often involved is Shikamaru. His intelligence could play a crucial role in any plot related to the Kazekage. And of course, the Sand Village elders might be important characters as they have influence over the Kazekage and the village's decisions.
Kakashi Hatake is often a main character in 'raikiri naruto fanfic' since he is the one who originally developed the Raikiri. His skills and the way he uses the Raikiri can be further explored in fanfics.
Naruto himself is often involved in Naruto seals fanfic. Since he's the main character in the original series, writers like to explore his potential with seals further. Sasuke is also a popular choice. His Uchiha heritage and his own power - hungry nature make for interesting stories when combined with seal knowledge. Kakashi is another one. His Sharingan and his vast knowledge of jutsu could lead to some really creative seal - related scenarios. And of course, Jiraiya, as he was a master of many things including seals, and his relationship with Naruto can be further developed in fanfic with a focus on seals.
Naruto himself is often involved. He might use bubblegum in his usual impulsive and creative ways, like coming up with new pranks or battle strategies. Sakura could also be a main character. She could use her intelligence to develop new types of bubblegum or figure out how to counter an enemy using bubblegum. Sasuke might be involved too, perhaps reluctantly at first, but then finding that bubblegum has some unexpected uses in his quest for power.
Kakashi can also be involved in some shukaku naruto fanfic. He could be Naruto's mentor in understanding the Shukaku better. He has a wealth of knowledge about the ninja world and could offer advice to Naruto on how to handle the power of the Shukaku and any potential risks associated with it.
Naruto is often involved. Since he's the main protagonist, writers like to put him in situations where he has to deal with deception, either being deceived or trying to deceive the enemy. Sasuke is also a common character in such fanfics. His complex personality and his past actions make him a great target for deception plots or a character who could be doing the deceiving.