In the fanfiction, perhaps Itachi trains Naruto to be able to counter the Akatsuki better. He could pass on his knowledge of the various Akatsuki members' abilities and weaknesses. Naruto, with his natural determination and Itachi's training, might develop new forms of the Rasengan or even learn how to use genjutsu more effectively, something he was not good at before.
One possible plot could be that Itachi, seeing Naruto's potential and his importance for the future of the Hidden Leaf, decides to secretly train him. Itachi might teach Naruto advanced jutsu, especially those related to chakra control and unique Sharingan - inspired techniques. Naruto, under Itachi's tutelage, would grow not only in power but also in his understanding of the ninja world's complex politics and the Uchiha clan's history.
The plot might involve Itachi training Naruto as a way to make amends for his past actions against the Hidden Leaf. Itachi could see Naruto as the key to bringing peace between the Uchiha and the village. So, he imparts his wisdom, combat skills, and strategic thinking to Naruto. Naruto, in turn, uses this new - found knowledge to unite the village further and face threats from outside forces more capably.
In this fanfiction, Itachi might also train Naruto in the ways of the Sharingan. Even though Naruto doesn't have the Sharingan naturally, Itachi could find ways to make Naruto understand the principles behind it, like how to read an opponent's movements more accurately. This could lead to Naruto having an edge in battles against opponents who rely on speed and deception.
In this fanfiction, Naruto might gain some unique jutsu skills from Itachi. Itachi is extremely powerful, so he could teach Naruto advanced genjutsu or ways to better control his chakra. For example, Naruto might learn how to quickly break free from strong genjutsu attacks, which would be a great advantage in battles against tough opponents.
The relationship between Naruto and Fem Itachi could be a very interesting aspect. They might form a strong bond similar to a master - apprentice relationship in traditional martial arts. Fem Itachi could share her own experiences and wisdom with Naruto, which could help Naruto better understand the world of shinobi, including the Uchiha clan and their secrets.
Well, it could be that Itachi trains Naruto to better control his chakra. Maybe Itachi sees potential in Naruto to bring peace to the ninja world and decides to pass on his unique skills like the Sharingan's insights on combat.
One aspect of the plot could be Naruto's struggle to control the new power. The Godlike Sharingan is a powerful and potentially dangerous ability. Naruto might initially have a hard time adjusting to seeing the world through the Sharingan's perspective. Itachi would then have to guide him through this process. Also, they could face enemies who are after the power of the Godlike Sharingan that Naruto now has, leading to intense battles where Naruto has to use his new skills and the knowledge Itachi has imparted to him.
Well, it could be about Naruto being forced into a dark situation where he has to train for killing. Maybe he's been misled or there's a great threat that makes him think this is the only way. For example, he might be tricked by an enemy who disguises as a friend and convinces him that the only way to protect the village is to become a killer.
Well, in such a fanfiction, Naruto might learn unique skills from the summons. For example, he could learn stealth from a cat - like summon or brute strength tactics from a bear - like one.
In the 'naruto trained seriously fanfiction', Naruto could be training with his friends in a more serious way. They might form a special training group where they push each other to their limits. For example, they could be training to improve their teamwork and combination jutsus. Naruto might focus on his speed and strength training while also learning how to better coordinate with his friends' abilities, like Sasuke's Sharingan - based attacks and Sakura's medical and combat skills.
In this fanfiction, perhaps Naruto could learn some unique jutsu from Asuma. Asuma was known for his wind - style jutsu, so he might teach Naruto advanced wind - style techniques that Naruto could incorporate into his Rasengan, creating a more powerful attack.
In the fanfiction, Naruto could also develop new strategies for fighting. Pein is a strategic mastermind, and under his training, Naruto might learn how to better analyze his opponents, anticipate their moves, and come up with more effective battle plans. This could give him an edge in future battles against powerful enemies.