One reason could be the trauma he experienced during the Wave mission. He might have seen the darker side of the ninja world, like the cruelty of Zabuza and Haku's situation. This could have made him more guarded and seemingly cold as he realizes the harsh reality.
As the daimyo, Naruto would face numerous difficulties. For starters, the cultural differences within the Wave Country itself could pose a problem. There might be different ethnic groups or regions with their own traditions that conflict with Naruto's plans for unity. Moreover, he has to deal with the after - effects of any previous wars or conflicts in the Wave Country. Rebuilding damaged areas and rehabilitating the affected people would require a lot of resources and careful planning. Additionally, he has to balance his ninja duties (if he still has them) with his new role as daimyo, which could be a real headache.
He may start to distance himself from his friends. Instead of being the overly friendly Naruto, he becomes more reserved. For example, he might not be as quick to join in on group activities or conversations.
Well, Naruto being the daimyo could bring a lot of positive changes. He might start by reforming the military system. Since he has his own ninja skills and experiences, he could train the local forces better. Also, he'd probably focus on improving the economy. For example, he could use his influence to get more trade deals with other countries. And in terms of society, he'd promote equality among all the people in Wave Country, regardless of their social status or origin.
In some fanfictions, Naruto becomes more confident after the Wave Mission. He realizes his own strength and the importance of his friends more deeply. For example, he might be more assertive in battles and decision - making.
Perhaps in this fanfiction, Naruto and his friends go back to the Wave Country for a follow - up mission. This time, they discover a new threat that is related to the power struggle they witnessed during the first mission. The group has to use their improved skills and teamwork to face this threat and protect the people of Wave.
Well, in certain fanfictions, Naruto's view of the ninja world as a whole can shift after the Wave arc. He might start to question the traditional ninja values. Since he witnessed the greed and corruption that led to the problems in Wave, he could strive to change the ninja world from within. He may begin to form his own ideas about what it truly means to be a ninja, which could be different from what he was taught at the academy. He could try to promote peace and cooperation more actively, rather than just following orders blindly.
If Naruto becomes a lich during the Wave arc in fanfiction, perhaps he'll have to deal with the moral implications of his new state. Liches are often associated with dark magic, but Naruto has a strong sense of right and wrong. He might struggle to find a balance between using his powers for good and not succumbing to the darker aspects of being a lich. Maybe he'll try to find a way to reverse the process while still using his powers to help his friends like Sasuke and Sakura.
In some fanfictions, Sakura might become more confident after the Wave mission. She realizes the harshness of the ninja world and starts to train harder, not just relying on her teammates. For example, she could be seen spending more time in the hospital, learning advanced medical ninjutsu to be more useful in future battles.
The main antagonist could also be a corrupt official within the Wave Country itself. After the events of the first mission, this official could have risen to power and now has plans to use his position to gain more control, even if it means going against Konoha. He could be secretly working with other villains or using his own resources to create problems for Naruto and his friends.