He could be motivated by a desire for revenge. Suppose something bad happened to him during his pregnancy that he blames on the traditional ninja system. He might see Akatsuki as a way to get back at the system that he feels has failed him. Also, he might believe that Akatsuki has the power to keep his unborn child safe from certain threats that he perceives in the ninja world.
The storyline would change drastically. Instead of following the path of protecting Konoha, Naruto would be involved in Akatsuki's missions. These missions are often related to capturing tailed beasts, which is the opposite of what he has been doing. So, there would be a complete reversal of his goals.
In this kind of fanfiction, Naruto might be neglected by his village. He could be feeling alone and unappreciated. So, he decides to join the Akatsuki. Maybe he sees them as a group that could accept him for who he is, regardless of his past in Konoha. He might start to learn their ways and use his skills for their missions.
Well, if Naruto and Tenten joined Akatsuki, it would be a huge shift in the Naruto universe. Naruto's ideals are so different from Akatsuki's. He believes in protecting the village and his friends, while Akatsuki is mostly about causing chaos and collecting the tailed beasts. Tenten, on the other hand, is a strong - willed kunoichi. Maybe they could try to change Akatsuki from the inside. But they would face a lot of opposition from the existing Akatsuki members who have their own agendas. It could lead to some really interesting power struggles and character development.
In a fanfiction where Naruto and Sakura join Akatsuki, it could lead to a complete shift in the power dynamics. They might initially be met with suspicion from the other Akatsuki members. Naruto could try to change the Akatsuki's goals from within, perhaps using his talk - no - jutsu to convince some of them to abandon their more villainous plans. Sakura, on the other hand, would bring her medical skills and combat abilities. This could also cause a rift between them and their former friends in Konoha, leading to some intense confrontations when they cross paths.
Well, one possible plot could be that they join initially to spy on Akatsuki from the inside. Naruto might think he can change the Akatsuki members' minds with his talk - no - jutsu. Sasuke could be there to find out more about the secrets Akatsuki is hiding, especially those related to his family. Maybe they end up causing chaos within Akatsuki as they slowly turn some of the members towards a more positive path.
It could be the Hidden Leaf Village itself. Since Naruto was neglected there, the village's leadership or some of the villagers who shunned him could be seen as antagonists. They pushed Naruto towards the Akatsuki by not giving him the support he needed.
Well, if Fem Naruto and Itachi don't join Akatsuki in the fanfiction, there would be a significant shift in character relationships. Sasuke's story would be completely different without Itachi's actions driving him. Fem Naruto could potentially form different alliances and rivalries. For example, she might team up with some other characters to deal with the threats that Akatsuki still poses without Itachi. Also, the Akatsuki's goals might be more easily thwarted without Itachi's strength and intelligence on their side.
Naruto joining Akatsuki would be a shock to many members. But some like Pain might see potential in him. Pain could view Naruto as a tool to achieve his goals or as a symbol of change within the organization. Naruto would try to convince Pain that there are better ways than destruction. Sakura's relationship with Kakuzu could be interesting. Kakuzu is all about money, and Sakura could use her knowledge of Konoha's economy to bargain with him. This could lead to a complex relationship where they are both trying to outwit each other while also having a certain level of respect for each other's skills.
A plot twist could be that Akatsuki has a hidden agenda that Naruto, Sasuke and Sakura are unaware of when they join. Maybe Akatsuki is being controlled by an even more powerful and sinister force, and the three are lured in as pawns. They then have to figure out the real situation and fight not only against the Akatsuki members who oppose their reform ideas but also against this hidden power.