In a smart Naruto and Sakura fanfic, Naruto's intelligence could cause him to take on more leadership roles. This would make him more responsible and mature. Sakura would see this change in Naruto and be inspired to grow herself. She might take on more teaching roles within the village, passing on her medical knowledge as well as the new ideas she's learned from Naruto. Their relationship would also evolve, becoming more of an equal partnership where they both contribute to each other's growth and the growth of the village.
A fanfic could start with Sakura being jealous of all the attention Naruto gets from other girls. As she tries to figure out why it bothers her so much, she discovers that she actually loves him. Then the story could be about her trying to find the right moment to confess her feelings.
A great fanfic idea could be that Sakura starts leaving little hints for Naruto about her feelings. She might cook him his favorite meal or offer to train with him more often. Naruto, being a bit dense in matters of the heart, doesn't quite get it at first. But as time passes, he begins to suspect that there's something more to Sakura's actions, and this could be the start of a beautiful love story within the fanfic.
Their relationship would likely be more complex in the past. Since they are from the future and already married, they would have a deeper connection. But they would also have to hide it from their past selves. Naruto might be more protective of Sakura in the past, and Sakura would be more confident in their relationship.
One possible plot could be that Naruto, being smart, quickly figures out a new and powerful jutsu. Sakura, impressed, decides to train with him more intensively. They go on a mission together where Naruto's newfound intelligence helps them outwit the enemy easily.
Naruto would likely become more diplomatic. His usual straightforward ninja approach might change as he has to deal with the complex politics of Rias's world. He would also gain a deeper understanding of different cultures. For Rias, she could become more empathetic. Naruto's past and his determination in the face of adversity might inspire her to be more understanding towards others. She might also learn some ninja skills from Naruto which could make her more versatile in combat.
Naruto's powers would evolve in a very different way. Aizen's training might focus on the psychological aspect of combat. So, Naruto's chakra control could be enhanced in a way that allows him to project his presence in a more intimidating way, similar to how Aizen can make others feel his overwhelming power. His ninjutsu could also be modified to have hidden elements, like a Rasengan that has a secondary effect that only activates when the opponent least expects it, just as Aizen has multiple layers of deception in his attacks.
Well, if Naruto is smart, he might be more confident in expressing his feelings to Sakura. He could use his intelligence to understand her better, like knowing what she really wants in a relationship. So, instead of the usual hesitations, he'd be more straightforward.
Sakura's evolution would be quite remarkable. She would start to think more like an Uchiha. Their way of analyzing situations and opponents would seep into her own mindset. This could make her more calculating and less impulsive in battles. Her physical strength, which she already has a good amount of, could be refined further with the training she gets from Shisui and Itachi. Her social standing in the village might also change as she is seen training with two of the most powerful and respected Uchiha. People would start to view her as a serious combatant as well as a healer, and she would have a greater influence on village matters related to security and combat strategy.
Sakura might react by being more assertive around Naruto. Instead of being shy or holding back, she could be more forward in showing her friendship or even her deeper feelings. She may also try to intimidate the fangirls in a way, like using her strength as a ninja to show that she is not one to be trifled with.
Sakura would likely be devastated. Naruto has been her friend and teammate for a long time. His death would leave a huge void in her life, and she'd probably go through a long period of mourning.