The Third Hokage's training might have introduced Naruto to more advanced jutsus. For example, he could have taught Naruto better control over his chakra, which is crucial for performing ninjutsu. This would allow Naruto to use his Rasengan more effectively and with less strain.
One challenge could be mastering difficult jutsus. The Third Hokage might set high standards for Naruto to learn complex techniques, which would be a struggle for him.
The main character, Uchiha Kirikyo, was the grandson of Uchiha Kyo and was also known as one of the twin stars of the leaf. After he became a Junin, he stayed in Kiba Hospital to develop, using the excuse of learning medical ninjutsu to paralyze the monitoring Dark Group. After five years, he had fully accumulated Monstrous Strength, Medical Ninjutsu, and Creation Regeneration proficiency. At the same time, he had also awakened the placement system. Placing it in different locations would allow him to gain proficiency in ninjutsu and blood inheritance. After his father's death, Shurakyuen proficiency +983. He inherited his father's will and sought Naruto's authority. I hope you like this fairy's recommendation. Muah ~😗
It could be an older version of Orochimaru who has also found a way to time travel. He might try to change the past to his advantage, like getting rid of the Third Hokage before he can become a threat to his future plans. Orochimaru is always power - hungry and his older self could be even more dangerous with knowledge of the future.
He would likely be seen as a traitor by the village. The villagers, who once saw Naruto as a hero - in - the - making, would now turn against him. He'd be hunted by the ninja forces of Konoha.
A possible plot is that the Third Hokage travels back to when he first became Hokage. He realizes all the mistakes he made in his first term and gets a second chance to do things right. He could focus more on training the younger generation, like Naruto and Sasuke's predecessors, in a better way. He could also be more proactive in dealing with external threats and internal conflicts, which would have a huge impact on the future of Konoha.
Well, it could be that the Sexy Jutsu has some sort of psychological effect on the Third Hokage. Maybe it reminds him of someone or something from his past that makes him hesitate. And in that moment of hesitation, Naruto is able to use the distraction to his advantage and defeat the Third Hokage. Also, Naruto might be able to use the jutsu in combination with other moves in the fanfiction. For instance, while the Third Hokage is distracted by the Sexy Jutsu, Naruto quickly follows up with a Rasengan.
One way this could be developed is if Naruto is somehow mind - controlled. For example, an enemy uses a powerful genjutsu on Naruto, making him lose his sense of self and see the Third Hokage as a threat to the village instead of a protector. Then, in his confused state, he attacks and kills the Third Hokage. This would create a huge moral and emotional conflict within the story, not only for Naruto when he comes to his senses but also for the entire village.
Sasuke could also be a possibility for the 6th Hokage in the fanfic. He has grown stronger over the years and his unique perspective on the ninja world could bring new ideas to the leadership of the Hidden Leaf. He might start off as a controversial choice but prove himself through his actions in protecting the village and making tough decisions.
Sasuke could be an alternative. He has strong ninja skills and a deep understanding of the ninja world. His experiences have made him grow into a very capable person, and his Sharingan gives him an edge in combat and strategic planning.