One good Sakura and Zetsu fanfic could be 'The Unlikely Alliance'. In this story, Sakura might find herself in a situation where she has to team up with Zetsu for a common goal. Maybe they are in a strange land and need to rely on each other's skills. Sakura's medical ninjutsu could come in handy when Zetsu gets injured, and Zetsu's knowledge of the area could help them navigate through difficulties.
Perhaps a new, powerful and mysterious ninja who has a vendetta against the Hidden Leaf Village where Sakura is from. He sees Zetsu as an accomplice of the village and targets both of them, causing chaos and danger in their lives. This new character could bring in a fresh and unexpected element of danger to the fanfic.
First, you need to understand the characters well. Sakura is strong - willed and has great medical skills. Zetsu has his own mysterious nature. Start with a unique concept, like maybe they meet in a parallel universe. Outline your plot, including how they interact, their conflicts, and how they resolve them.
One idea could be that Zetsu discovers Sakura's hidden power during a mission, and they form an unlikely alliance. This alliance then leads to them exploring new areas together and facing various challenges as a team.
One common theme could be forbidden love. Since Zetsu has his own nature in the Naruto world and Sakura is a shinobi, their relationship might be seen as something that goes against the norms. Another theme could be the exploration of their different powers in relation to each other. For example, how Sakura's medical ninjutsu could interact with Zetsu's unique abilities.
One interesting sakura and zetsu fanfiction could be about them teaming up on a mission in a different dimension. They might face new and strange enemies, and through their combined efforts, they learn to understand each other better.
One possible plot could be that Zetsu, with his unique abilities, somehow crosses paths with Sakura. Maybe he's on a mission related to the Akatsuki and she gets in his way. He could initially view her as just another obstacle, but as time goes on, he realizes her strength and tenacity. This could lead to an unlikely alliance where they work together to achieve a common goal, like saving a village from a greater threat.
Zetsu could be sarcastic towards Sakura, taunting her about her human emotions. Sakura, in turn, would stand up for herself and show her strength. For example, Zetsu might say something like 'Your soft heart will be your downfall, little girl' and Sakura would reply 'My heart is what makes me strong, something you could never understand.'
Naruto could be the one to save her. He has a strong bond with Sakura and would never let her be in danger for long. His powerful ninja skills and his unwavering determination would make him a likely candidate to rescue her from Black Zetsu's grip.
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.