Naruto would likely become more secretive. Since Orochimaru is a very private and often devious character, Naruto might pick up some of those traits. He would probably keep things from his friends more often.
Well, in such a fanfiction, Sakura being Orochimaru's apprentice could lead to some really interesting character developments. For one, Sakura would likely gain a darker and more ruthless edge to her skills. Orochimaru is known for his unethical experiments and dark jutsu. Sakura might learn some unique medical ninjutsu from him that goes against the normal ethical boundaries in the ninja world. It could also put her in a conflicted position with her former teammates, especially Naruto and Sasuke. They might view her new association with suspicion and it would create a lot of drama and tension in the story.
They would develop in terms of their skills. Under Orochimaru, they would gain a lot of knowledge about chakra manipulation and forbidden jutsu. But with Naruto, they would learn about the power of bonds and friendship. This combination could lead to the development of new jutsu that combines both physical power and the strength of relationships. Also, they would grow in their understanding of right and wrong, as Naruto's moral compass would constantly be in conflict with Orochimaru's more amoral stance.
The apprentice could learn unique jutsu from Orochimaru. Since Orochimaru is known for his forbidden jutsu, the apprentice might gain an edge in combat but also face the danger of being corrupted by the power. They could then use these skills in battles against common enemies. And, in the process, they might try to redeem Orochimaru in some way, like showing him that there is a better path than his thirst for power.
He might learn Orochimaru's signature snake - related jutsu, like the Hidden Shadow Snake Hands. This jutsu allows the user to summon snakes from their sleeves or other hiding places to attack opponents.
Naruto's character would likely be darker. Orochimaru is known for his unethical experiments and thirst for power. Naruto, under his tutelage, might be more focused on individual strength rather than the bonds he values in the original series. He could become more secretive and less trusting of others.
One possible plot is that Orochimaru needs Sakura's medical skills for one of his experiments. He kidnaps her and forces her to be his apprentice. Sakura initially resists but realizes that she can learn a great deal from him. As she becomes more involved in Orochimaru's world, she starts to form her own plans. She could be secretly working on a way to use Orochimaru's resources to develop a cure for a deadly disease in the ninja world. But she has to keep her true intentions hidden from Orochimaru, leading to a tense and complex plot full of twists and turns.
One possible plot development could be Naruto struggling with Orochimaru's dark teachings while still holding onto his own sense of justice. Maybe he tries to find a way to use Orochimaru's knowledge for good. For example, he could learn some unique jutsu from Orochimaru and then modify them to be less harmful or more in line with Konoha's values.
Naruto's development would be a journey of self - discovery. As Orochimaru's apprentice, he would be exposed to different forms of power and knowledge. He might initially be disgusted by Orochimaru's methods but then realize that he can use some of it for good. His social skills would change too. He would be more adept at dealing with enemies and those with different motives. His sense of humor might even change, becoming darker to fit in with Orochimaru's crowd. But deep down, his core values of friendship and protecting the weak would still be there, just masked by his new persona as Orochimaru's apprentice.
One popular storyline could be the apprentice learning unique jutsu from Naruto. For example, they might learn his Rasengan technique in a more in - depth way, with Naruto guiding them through every step of the process.