Well, a plot could revolve around Naruto being in a situation where he has to keep a big secret from his friends, just like Itachi did. This could create a lot of internal conflict for Naruto. He might start to isolate himself, which his friends would find strange. Also, in terms of power, Naruto could be exposed to a power similar to Itachi's Mangekyo Sharingan. He would have to learn to control it without losing himself, and this could be a great arc in the fanfiction. It would show Naruto's growth as he struggles with the new power and the implications of using it.
A possible plot is that Naruto is sent on a mission to infiltrate an enemy organization, much like Itachi infiltrated the Akatsuki. He would have to pretend to be on their side, all while trying to gather information to protect Konoha. During this time, he could adopt Itachi's stoic and observant nature. He might also face moral dilemmas similar to Itachi's, such as whether to kill an enemy who could potentially be redeemed. This would force Naruto to question his own beliefs and values, and how far he is willing to go for the greater good, just like Itachi did in the original story.
Maybe Itachi is on a secret mission outside of Konoha and he saves Naruto from a group of rogue ninjas. Naruto, being Naruto, is immediately drawn to Itachi's strength and kindness. They start to train together in secret. As they train, Naruto discovers Itachi's past and the burden he carries. This leads to Naruto vowing to help Itachi find a way to clear his name in Konoha and they become close friends in the process.
A great plot could be Itachi teaching Naruto how to control the Nine - Tails' chakra in a completely different way than Jiraiya did. Since Itachi has such a deep understanding of chakra and its nature, he could offer unique insights. Also, there could be a story where Itachi and Naruto are forced to team up against a common enemy that is using an ancient and powerful jutsu. In the process, Itachi passes on some of his Uchiha clan's wisdom to Naruto. And perhaps, Itachi could help Naruto deal with the loneliness that often comes with being a jinchuriki, as Itachi has also felt isolated in his own way.
One idea could be that Naruto discovers Itachi's true motives early on. So instead of seeing him as an enemy, he tries to help Itachi with his mission in the Akatsuki secretly. They could meet in secret places and exchange information about the Akatsuki's plans and how to protect the Leaf Village at the same time.
One idea could be Itachi discovers Baby Naruto has a unique chakra signature that could change the future of the ninja world. So, he decides to secretly protect Naruto from afar. Another could be Itachi is tasked with a mission that involves Baby Naruto in some way, like having to test Naruto's potential without the village knowing. And a third could be Itachi has a vision of a future where Baby Naruto is the key to peace, and he starts to subtly influence Naruto's growth even at that young age.
One plot idea could be that the OC is initially scared to tell Itachi about the pregnancy. She might worry about how it will affect his mission or his standing in the ninja world. Another could be that Itachi, being the protective type, goes to great lengths to keep the OC and the unborn child safe from his enemies. He might even consider leaving his organization to ensure their safety.
One idea could be that baby Naruto somehow crosses paths with Itachi in a secret mission. Maybe Itachi is on a mission in Konoha and stumbles upon baby Naruto who has an unusual chakra flare. Itachi, being curious, decides to keep an eye on him without revealing himself. This could lead to a series of events where Itachi's actions unknowingly protect Naruto from some early threats.
One idea could be that Itachi survives his battle with Sasuke and teams up with Naruto to face a new, powerful enemy from the Otsutsuki clan. They combine their unique skills, Naruto's Rasengan and Itachi's Sharingan abilities, to take on this threat.
A possible plot could involve Female Itachi being an outcast in her own clan because she has different ideals. Naruto, who always believes in people, befriends her. They then start a journey to prove that her ideas can bring peace to the ninja world, facing opposition from both their own and other clans.
One idea could be a story where baby Itachi meets a young Naruto in a sort of alternate universe. Maybe Naruto stumbles upon a hidden place where baby Itachi is being kept safe. They form an unlikely friendship, and Naruto's positive energy starts to influence Itachi in a way that makes him question some of the darker paths he might take in the future.
One idea could be exploring Itachi's time in ANBU and how Naruto might have influenced his decisions secretly. Maybe Naruto, with his unique way of seeing people, could have made Itachi question his path in the ANBU more deeply.