Perhaps the female shinigami trains Naruto to have a better understanding of life and death. In the Naruto world, death is a significant concept, and with the shinigami's training, Naruto could become more in tune with the cycle of life and death. This might lead to him being able to communicate with the spirits of the dead, getting advice from past Hokages or his parents in a more profound way.
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.
The plot might involve Naruto being sent to the Shinigami realm for some reason. There, he has to adapt to the rules and powers of the Shinigami. He could make allies among the Shinigami and bring back some of their knowledge and powers to his own world, causing a stir among the ninja clans. He might also face challenges from Shinigami who don't trust him at first because he's an outsider.
One possible plot development could be Naruto learning some of Orochimaru's unique jutsu. For example, he might pick up on Orochimaru's snake - related techniques. This could give Naruto an edge in combat against opponents who are not familiar with such unorthodox attacks. Also, Orochimaru's knowledge of forbidden jutsu might be passed on to Naruto in a modified, less dangerous way, which could then be used to surprise his enemies in future battles.
Well, in this fanfiction, perhaps the female Kyuubi has a special connection with Naruto. She might train him not just in physical combat but also in mental strength. She could expose Naruto to illusions that are based on her own experiences as a powerful being. Through this, Naruto learns to break free from powerful mental restraints and becomes even more confident in battle.
Well, it could involve a character making a deal with a Shinigami. Maybe a ninja is on the verge of death and in order to gain some extraordinary power to save their village or loved ones, they make this contract. The Shinigami might demand something in return like a part of their soul or their future memories.
In such a fanfiction scenario, Naruto might gain some really unique powers. The Shinigami could teach him about different forms of spiritual energy which could enhance his already formidable chakra. Maybe he'd learn to manipulate souls or gain a new level of perception.
One possible plot could be that the female Naruto has to overcome the initial disbelief and discrimination within the village. Tsunade, seeing her potential, takes her under her wing. She trains her not only in physical combat like the Rasengan but also in medical ninjutsu. As she grows stronger, she faces off against new threats to the village, using her unique combination of skills learned from Tsunade and her own natural tenacity. Eventually, she earns the respect of the entire village and becomes a great ninja like her male counterpart was in the original series.
Well, in many such fanfictions, a key plot development is Naruto's enhanced combat skills. Since he's trained by toads, he might learn new jutsu like more powerful toad - related techniques. His relationship with the toads also deepens, and this could lead to him having a better understanding of the Sage Mode. Maybe he discovers new ways to combine his regular ninjutsu with the toad - based training. Another aspect could be his growth in terms of leadership. As he gets stronger, he might inspire other characters in the fanfiction to follow his lead more, which in turn could change the dynamics of battles or the overall story's progression.
One possible plot could be that Naruto makes a deal with the Shinigami to gain more power to defeat a powerful enemy. In exchange, he might offer his own lifespan or something precious to him. Maybe he needs this power to save his village from a new, overwhelming threat like an ancient evil that has awakened.
In a fanfic where Naruto is trained by the Shinigami, Naruto would face a whole new set of challenges. The training would be tough as the Shinigami's methods are likely to be very different from what he has experienced before. He might have to endure tests that involve facing his inner demons or dealing with the power of death directly. This could lead to a significant character development for Naruto. He would not only become stronger physically but also mentally, as he grapples with the complex concepts associated with the Shinigami's realm.