Orochimaru is another possibility. He is already somewhat of an evil genius in the original Naruto series. In a fanfiction, he could be further developed as the main character, perhaps with his experiments taking on even more extreme and far - reaching consequences. His actions and plans could be the central focus of the story, with other characters either trying to stop him or being caught up in his schemes.
Well, Naruto is obviously one of the main characters. But there could also be other characters like Sasuke. Sasuke might be either an ally or an adversary to Naruto's 'evil genius' plans. He could be trying to stop Naruto if he thinks Naruto has gone too far into the 'evil' territory, or he could be working with Naruto for some mutual, albeit more self - interested, goals.
Tenten could potentially be in the harem. She is a strong - willed and capable kunoichi. Her presence in the harem could add an element of action and adventure. Maybe she initially tries to fight against the evil Naruto but then gets drawn into his world and eventually becomes part of his harem.
It's possible that a group of students could be the main characters. They all learn from the genius sensei in different ways. One student might be great at physical combat, another at ninjutsu, and they have to work together under the sensei's guidance. Their combined growth and how they interact with each other and the sensei can form the core of the 'naruto genius sensei fanfic'.
A new, original character could be the main character in a Naruto chains fanfiction. This character could be from a small, unknown ninja village and possess a unique ability to control chains made of some special material. They could come to the Hidden Leaf Village and get involved in the events there, interacting with the well - known Naruto characters.
It's hard to say without reading it, but it could be Naruto himself if the story is about a secret aspect of his genius that hasn't been explored in the original. Maybe he has some hidden intellectual ability that is only revealed in this fanfiction.
There could be original characters created specifically for this fanfiction. Maybe a mysterious mentor figure who helps Naruto understand and control his 'dark genius' side. This character could have their own backstory and motives that tie into the overall plot.
Even Naruto himself could be a subject of this 'evil Hokage' concept in fanfiction. Maybe he is possessed by some dark entity or has a major change of heart due to some extreme event. This would completely change his character and turn him into an evil Hokage, which would be a very interesting and unexpected twist.
There could also be new characters introduced as antagonists. In this fanfiction, perhaps there are dark entities that are either drawn to Naruto's new evil self or are competing with him for control. They might have powers that rival or complement his Rinnegan - based abilities, leading to some intense battles and power struggles.
Well, obviously Naruto and Hinata are the main characters. Naruto is the protagonist with his strong will and determination. Hinata, in this case, is the one with an evil turn, which makes her a central figure as well.
Obviously Naruto would be one of the main characters. There might also be his friends like Sasuke and Sakura, but they could be portrayed differently since Naruto is 'evil' in this fanfiction. Maybe there are also some original characters created specifically for this fanfic that are related to the gaming aspect, like a mysterious game master who is manipulating Naruto's actions.