The OC could be designed as a very empathetic person. Since Sasori has a lot of emotional baggage from his past, an empathetic OC can understand his feelings and help him heal. For example, she could listen to his stories without judgment and offer comfort.
A possible plot could involve a situation where Sasori has some sort of valuable information that the Leaf Village needs. Naruto, being the bold and unpredictable one, decides to impersonate Sasori to get close to the source of that information. He might have to use his shadow clones to create the illusion of Sasori's puppet - like abilities. And during this impersonation, he could learn more about Sasori's past and what made him the way he was, while also trying to achieve the mission goal without getting caught.
I'm not sure of a specific 'naruto impersonates sasori fanfic' off the top of my head. You could try searching on fanfic websites like Fanfiction.net or Archive of Our Own. They have a large collection of Naruto - related fanfictions and you might be able to find one there.
One interesting Sasori x Naruto fanfic could be 'The Unlikely Bond'. In this fanfic, Sasori, with his cold and mechanical nature, gradually forms an unexpected connection with Naruto's warm and determined personality. It might explore how their different outlooks on life and their respective powers interact in unique ways.
One common theme is redemption. Often, Fem Sasori is portrayed as a character who has a chance to atone for her past actions through her interactions with Naruto. For example, she might have been a villain before but Naruto's positive influence changes her.
Maybe in the fanfic, Naruto is on a mission to retrieve some important information that Sasori has. When Naruto talks to Sasori, it turns into a battle of wits. Sasori tries to deceive Naruto with false information while Naruto uses his intuition and sharp mind to see through the lies. Along the way, they also discuss their different upbringings and how it shaped their current selves.
In this fanfiction scenario, Naruto would bring his own unique fighting style. He's got his shadow clones and Rasengan. Sasori is a tough opponent with his puppet army. Naruto might struggle at first to deal with the puppets' various attacks. But with his determination and quick thinking, he could find a way to get close to Sasori and use his Rasengan. It would be an intense battle, different from the one Sakura had with Sasori, as Naruto has a completely different set of skills and strategies.
One common theme is the idea of redemption. Sasori, with his past as a villain, often finds redemption through his relationship with Naruto. Another theme is the exploration of their different worlds colliding. Naruto's positive outlook and Sasori's more jaded view make for an interesting contrast.
It could still be Orochimaru. Even though the focus is on Naruto and Sasori talking, Orochimaru might be pulling strings in the background. He could be using Sasori's connection to Naruto to further his own evil plans, like getting access to some powerful jutsu that Naruto might possess or know about.
You could also check out Naruto fanfic review blogs or YouTube channels. Some bloggers or YouTubers review and recommend fanfics. They might have a section dedicated to Sasori x Naruto fanfics. This way, you can get an idea of which ones are worth reading before you start.