In this kind of fanfiction, Itachi might use his powerful Sharingan abilities. He could perhaps create illusions to mislead Orochimaru and his minions, then quickly snatch Sasuke away. For example, he could make Orochimaru think that Sasuke is in a completely different location while he secretly approaches and rescues him.
It shows the strong bond between the two brothers. Despite all the complications in their relationship, Itachi still cares deeply for Sasuke and is willing to risk a lot to save him from a great danger like Orochimaru.
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 fanfiction could involve Itachi being possessive over Sakura in a way that is born out of his need to protect her. He might see her as a symbol of hope or something precious in a dark world. Maybe he secretly watches over her, using his skills to keep her out of harm's way without her knowledge at first.
Perhaps Itachi realizes that Naruto has the potential to change things for the better in the ninja world. He takes Naruto with him to train him in ways that the Leaf Village couldn't. Itachi may have some knowledge or skills that he wants to pass on to Naruto, like how to deal with the power of the Nine - Tails in a more efficient way.
Itachi might have a secret agenda that Kisame is not fully aware of. He could be using this opportunity to protect Naruto in some way while still appearing to be following the Akatsuki's orders. So, there could be a lot of internal conflict within the Akatsuki duo during this whole situation with Naruto.
In some Orochimaru lemon fanfic, he might be portrayed as having a more seductive or alluring side. However, this is a very unorthodox view compared to his original character in the Naruto series. His intelligence and cunning nature might still be emphasized, but in a more sexually charged context which is not really in line with the official Naruto story.