Maybe the fanfic could start with the OC being experimented on by Orochimaru. Naruto and Itachi somehow cross paths with the OC. Itachi, seeing the OC's situation, decides to help, which leads to a complex relationship between them all as Naruto tries to understand Itachi's motives and the OC tries to break free from Orochimaru's control.
First, you need to develop your OC well. Give them a unique backstory, personality, and goals. For example, if your OC is a ninja, what are their special abilities? Then, think about how they interact with the existing characters. With Orochimaru, it could be a relationship of fear or mentorship. With Itachi, perhaps respect or a family - like bond. For Naruto, it could be friendship. Also, have a clear plot. Maybe the OC is caught in the middle of a power struggle between Orochimaru and those who oppose him, and Itachi and Naruto are on different sides of this struggle.
One possible title could be 'Itachi Uchiha and the Unseen Bond with the OC'.
A fanfic could revolve around an OC who is a former disciple of Orochimaru. This OC realizes the evil of Orochimaru's ways and decides to defect. The story could then be about the OC's journey to redeem themselves and stop Orochimaru from carrying out his next big, diabolical plan. They might team up with some of the main Naruto characters to achieve this.
One idea could be a story where Sakura, as a skilled medic, is tasked with treating Itachi and Shisui during a difficult mission. She discovers their complex pasts and bonds with them over time, leading to new alliances and friendships.
One idea could be a story where Itachi and Kushina meet in a parallel universe. In this universe, the events of the original Naruto storyline are altered, and they end up on the same side, fighting against a new common enemy. Their unique abilities, Itachi's Sharingan and Kushina's powerful chakra, would make for an interesting combination in battles.
One idea could be a story where Naruto and Haku team up on a special mission. They could start off not trusting each other much, but as the mission progresses, they come to respect and rely on one another's skills. For example, Naruto's brute strength combined with Haku's stealth and water jutsu could make for an interesting dynamic in overcoming the mission's obstacles.
First, you should focus on Itachi's character traits. His calm and calculating nature, his loyalty to his clan despite the difficult decisions he had to make. For the OC, give her (or him) a unique backstory that can connect with Itachi's world. Maybe the OC has a special power that Itachi notices.
One idea could be a story where an OC (original character) teams up with Jedi Surik and Aayla on a mission to rescue a group of younglings. The OC could bring in a unique skill set, like being a master of an ancient form of combat that helps them overcome the challenges along the way.
There's also 'The OC's Journey with Itachi'. This fanfiction focuses on how the OC's presence changes Itachi's perspective on certain things. The writing style is captivating, and the author does an amazing job of creating a believable relationship between Itachi and the OC. It has some really heart - warming moments.
The theme of identity is quite prevalent as well. An Uchiha oc in a fanfic may question who they are, especially considering the unique nature of the Uchiha clan. Are they defined by their clan, by their powers, or by their own individual choices? This internal conflict is often explored in great detail, making for a very engaging read.