Black Zetsu's story in Naruto is quite the tale. He was an entity that had been around since ancient times. He had an in - depth knowledge of the ninja world's history and used this to his advantage. He was the driving force behind many of the conflicts in the Naruto series. For example, he caused a rift between Sasuke and Naruto at times. His true nature was only revealed towards the end of the series, which was a shock to many characters. He was a master of manipulation, using the desires and weaknesses of others to achieve his ultimate aim of bringing back Kaguya.
One key event was his deception of Madara. He made Madara think he was his ally while actually setting him up for Kaguya's revival. Another was his influence on Obito. He pushed Obito to do things that served his purpose. Also, his role in the Fourth Great Ninja War was significant as he was behind many of the unexpected turns in the war.
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.
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.
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.
When Naruto absorbs Zetsu in the fanfiction, it could impact his mental state as well. Zetsu has been involved in many dark and devious plans. Naruto might have to struggle with the knowledge and influence of those. However, on the positive side, Naruto could use Zetsu's ability to communicate with the plants and gather intelligence from the natural world. This would expand his range of information sources and give him an edge in strategic planning during battles.
He may develop a more calculating side. Black Zetsu is all about manipulation. Naruto could start thinking several steps ahead in a more devious way. For example, he might start using people's weaknesses against them, which is completely against his original nature. This change in personality would likely cause a rift between him and his friends who know him as the always - honest and straightforward Naruto.
It could change his relationship with Sakura. Sakura might be a bit wary of Naruto at first because of the unknown effects of absorbing Zetsu. But as she sees that Naruto is still the same person at heart, she would gradually accept him again. With Kakashi, he might be more cautious and keep a closer eye on Naruto to make sure he doesn't lose control.