There could be an original character created in the fanfiction who has a unique form of the Rinnegan. Maybe they have combined it with another kekkei genkai, making them a powerful force. Such a character could have abilities that are unheard of and thus be one of the most powerful.
The OC's Rinnegan in a Highschool DxD fanfiction would be extremely powerful. It could give the character abilities like seeing through illusions, which would be very useful against devils known for their trickery. The power to summon creatures from the Six Paths could also be a game - changer. It could summon powerful beings to fight alongside the OC in battles against other supernatural entities in the DxD world.
There are some great plotlines in rinnegan naruto fanfics. For example, in 'Naruto's Rinnegan Awakening', the plot is centered around how Naruto awakens the rinnegan and how it changes his relationships with his friends and enemies. Some of his friends are scared of his new power, while some enemies see him as an even greater threat. In 'The Rinnegan and Naruto's True Purpose', the story is about Naruto realizing that his rinnegan gives him a new purpose in life, not just to protect the village but to unite all the shinobi clans. And in 'Rinnegan Naruto: Beyond the Limits', the plot follows Naruto as he pushes the limits of his rinnegan powers, going beyond what anyone thought was possible and facing the consequences of his actions.
Kakashi can be quite popular too. His wisdom and experience could play a role in guiding Naruto as he deals with the power of the Rinnegan. Also, fans might be interested in seeing how Kakashi reacts to Naruto's new - found power and how it might affect their bond.
It could be interesting to see Naruto with both EMS and Rinnegan in fanfiction. Naruto is known for his Uzumaki vitality and his ability to master new powers quickly. Having EMS and Rinnegan would give him an entirely different set of skills. He could combine the Rasengan with Rinnegan - based techniques and use the EMS - enhanced perception to dodge attacks even better. His positive attitude and never - give - up spirit would make for an exciting exploration of these powers.
One interesting storyline could be Dark Naruto using the Rinnegan to reshape the ninja world according to his own dark vision. He might start by taking over hidden villages one by one, using the powers of the Rinnegan like the ability to summon powerful creatures or manipulate gravity. Another could be his interaction with other powerful characters. For example, how he would deal with Sasuke, who has his own set of powers and goals. It could lead to epic battles and power struggles.
Pain is often a very popular character in Rinnegan fanfiction. His original use of the Rinnegan in the series made him quite an interesting character, and in fanfiction, people like to explore his backstory further or give him new powers. Nagato, who was the original owner of Pain's body, is also popular. He has a complex history and his connection to the Rinnegan can be explored in many ways.
Well, Obito Uchiha can also be considered an iconic character in Rinnegan - related fanfictions. His connection to the Sharingan and his later acquisition of the Rinnegan through various means is a rich area for exploration. And, there could be an ancient ancestor of the Rinnegan Clan, a character only mentioned in the fanfiction, but whose legend looms large over the clan and its members.
Sasuke Uchiha is often a popular choice. Given his natural Uchiha abilities and his connection to the Rinnegan in the original Naruto story, he's a likely candidate in fanfiction. His brooding nature and quest for power make him a great character to explore further with the added power of the Eternal Rinnegan.
The Akatsuki as a whole could be antagonists. In fanfictions, the Akatsuki might be interested in the power of Naruto's Evil Rinnegan. They could try to capture him to extract the power or use him in some way for their own goals. Pain, being a powerful member of the Akatsuki, could also be a specific antagonist. His own ideology about pain and peace might clash with Naruto's new, potentially more chaotic state with the Evil Rinnegan. Additionally, new original antagonists created specifically for the fanfiction could be common. These could be dark, powerful figures who are drawn to the power of the Evil Rinnegan and want to either possess it or destroy Naruto to prevent its misuse.