An OC (original character) could be a godlike assassin. This gives the author complete freedom to create a character with the perfect set of skills, a mysterious background, and a unique personality. They could have powers like teleportation or the ability to control time briefly, which would make them extremely powerful and godlike in the Naruto universe.
Well, in a 'naruto godlike assassin fanfiction', the combination of the Naruto world's existing elements with the assassin concept is appealing. The Naruto world has a rich culture, jutsus, and clans. When you add the stealthy and deadly assassin aspect, it creates a new and exciting dynamic. The assassins can use Naruto - style techniques in their own sneaky ways, like using shadow clones to deceive enemies while they strike from the shadows.
Jiraiya could be an interesting assassin master. He already has a lot of knowledge and skills that he could pass on to Naruto in a more assassin - like way. His experience in espionage and combat would make him a great fit.
It could be Sakura. Maybe she becomes envious of Naruto's newfound godlike status. She might feel that he has changed too much and is no longer the Naruto she knew. So, she could side with those who want to bring Naruto down, either out of jealousy or a misguided sense of what's right for the village.
Sasuke could be a likely candidate in a sense. Given his skills as a ninja, his Sharingan which gives him an edge in combat and perception, and his past as a sort of 'rogue' ninja. He could be in a situation where Naruto has to hire him for a special mission that requires his unique abilities. Another possibility is Kakashi. He has a vast array of skills, is very intelligent, and could easily take on the role of an assassin if needed, even if it goes against his normal moral code slightly. He would do it for Naruto's sake.
Sakura could be in the harem. She has always had a connection with Naruto, and his new godlike status might make her see him in a different light. Hinata is also a likely candidate, as she has always been in love with Naruto. And perhaps some new female characters could be introduced, like a powerful kunoichi from a far - off land who is drawn to Naruto's power.
Maybe it's Naruto himself with an additional power - up. Imagine Naruto gaining the godlike lightning ability on top of his existing powers. He would be even more formidable and could use the lightning in combination with his shadow clones and Rasengan techniques. This would change the dynamics of his battles and relationships with other characters like Sasuke, who also has powerful lightning - based attacks.
It could be a completely new character created just for this fanfiction. Maybe a child with some unique abilities that Naruto discovers and decides to take under his wing.
Perhaps there are dark forces from another dimension. These forces might be attracted to Naruto's power and want to either steal it or destroy him to prevent him from using it against them. They could be powerful demons or sorcerers with their own motives.
It could be a combination of Orochimaru and Lex Luthor. Orochimaru from the Naruto universe is always seeking power and Lex Luthor from the DC universe is a brilliant but evil mastermind. They could team up, with Orochimaru being interested in Superman - like Naruto's unique physiology and Lex Luthor wanting to use Naruto's power to take over both the Naruto world and the DC world. They would be a formidable duo, constantly devising plans to undermine Naruto and his friends.
It could be a new group of rogue shinobi who have been causing chaos in the ninja world while Naruto was away. They might have targeted Naruto's friends or family, which is why he's back for revenge.