I'm not sure specifically as there could be many different interpretations in fanfiction. But it might involve Zetsu using his unique abilities to rescue Naruto from a dangerous situation, like a powerful enemy attack or a life - threatening trap.
Well, one way could be in their physical abilities. Maybe in the fanfic, Naruto is shown to have some of Zetsu's stealthy movement skills, like being able to blend into the environment in a similar way. Another similarity could be in their connection to nature. Zetsu has a strong link to the plant - like aspects of nature, and Naruto's chakra might be shown to have a similar kind of connection in the fanfic.
Well, one possibility could be that Zetsu imparts some unique and dark jutsu to Naruto. Maybe Naruto starts to learn stealth and subterfuge skills from Zetsu, which are different from what he learned at the ninja academy. This could lead to Naruto having an edge in certain battles where traditional ninja skills aren't enough.
There could be internal antagonists within Naruto's own village. Some of the more conservative ninja in the village might not trust Naruto's new - found skills and powers obtained from Zetsu. They could try to undermine Naruto or even attempt to exile him, fearing that he has been corrupted by Zetsu's teachings.
Obviously, Naruto and fem Zetsu are the main characters. Naruto, with his determination and dream of becoming Hokage, is the protagonist we all know. Fem Zetsu, on the other hand, brings her own unique set of abilities and a different perspective, being a part of the Zetsu race which has its own mysteries in the Naruto universe.
One interesting Naruto and Female Zetsu fanfiction could be one where they team up for a mission. In this story, Female Zetsu might use her unique abilities to help Naruto in a difficult situation, like sneaking into an enemy base. They could develop an unexpected friendship during the process.
Naruto himself is a great choice. Their personalities are so different that it can create a lot of interesting interactions. Naruto's positive and determined attitude can contrast with fem Zetsu's more mysterious nature.
There could be a fanfiction where fem Zetsu forms an unlikely alliance with Naruto. Maybe she sees something in Naruto that makes her want to change her ways. In this story, they could go on adventures together and she could learn about friendship and loyalty from Naruto. This would be a great way to explore her character in a new light.
It's likely that Naruto's chakra control and power would develop in new and unexpected ways. Black Zetsu might introduce him to strange chakra - based abilities that are not part of the normal ninja training. This could give Naruto an edge in combat, but it also might make him a target. Since Black Zetsu has his own motives, Naruto could be dragged into some dangerous and complicated situations that he may not be fully prepared for.