In a different scenario, the female Naruto joins Orochimaru out of a sense of adventure. She thinks she can handle whatever Orochimaru throws at her. As she trains under him, she begins to understand the true nature of his ambitions which are far more sinister than she expected. She tries to influence Orochimaru to change his ways using her own positive outlook on life. But when that fails, she has to fight her way out, using the skills she learned from him against him.
Perhaps the female Naruto joins Orochimaru because she wants to learn more about the secrets of the ninja world that she believes Orochimaru can unlock. She may be curious about the darker aspects of ninjutsu that are not taught in the normal ninja academies. But then she discovers that Orochimaru is using her for his own immoral experiments. She then teams up with some of Orochimaru's former followers who also want to break away and they plot to take him down from the inside.
Well, perhaps Naruto and Sasuke are forced to join Orochimaru. Maybe Orochimaru has some kind of leverage over Konoha that makes them comply. In this fanfiction, they could start to learn unique jutsus from Orochimaru but also have to constantly resist his more evil intentions. They might also meet some interesting characters within Orochimaru's lair.
A possible plotline could be Orochimaru's redemption. He realizes the error of his ways and joins Naruto in protecting the ninja world. He could use his vast knowledge of jutsu and forbidden arts to help Naruto against new threats.
One possible plotline could be Naruto being forced to serve Orochimaru due to some sort of blackmail or threat against his friends in Konoha. Maybe Orochimaru has some information that could endanger Naruto's loved ones if he doesn't comply. Another aspect could be Naruto initially pretending to serve while actually trying to find a way to take Orochimaru down from the inside. This would add an element of mystery and deception to the story.
Perhaps Naruto starts to have a connection to Orochimaru's other experiments or creations. He might find himself in a situation where he has to either help or fight these other 'products' of Orochimaru's mad science. Also, the fanfiction could explore how Naruto's friends react to what has happened to him. Do they trust him still? Or are they afraid of what Orochimaru might have turned him into?
Another plotline could be that Orochimaru is forced to train Naruto. Maybe the Hidden Leaf Village has some sort of leverage over Orochimaru. During the training, Naruto discovers some dark secrets about Orochimaru's past and his experiments. This knowledge could help Naruto in his future battles not just against Orochimaru if he turns on him, but also against other enemies who might have similar ideas. Naruto might also gain some new physical abilities from Orochimaru's training, like enhanced speed or strength.
In this fanfiction, Naruto might join Madara because of some sort of time - travel or alternate reality situation. He could find himself in a world where Madara's actions seem more justifiable. Naruto, being Naruto, would still strive for peace. So he might try to guide Madara towards a more peaceful solution while being part of his group. This could create a really unique dynamic where Naruto is constantly trying to nudge Madara in the right direction while also dealing with the other members of the group who may not be as open to change.
One possible plotline could be that Naruto, heartbroken from a failed relationship or the loss of a dear friend, throws himself into the dangerous and secretive world of ANBU to numb his pain. He might start off as a reckless agent, but gradually find purpose in protecting the village in a more covert way. This could lead to him making new, deeper friendships within the ANBU ranks.
Another plotline could be a more psychological exploration. Orochimaru has always been a bit of an enigma, and his love for Naruto could be a way to explore his own humanity. Maybe he has a change of heart because of Naruto and starts to question his past actions. This could lead to a journey of self - discovery for Orochimaru, while Naruto is left to figure out how to deal with this new side of his old enemy.
Well, in such a fanfic, a plotline might involve Naruto's friends trying to rescue him. They could discover Orochimaru's lair where Naruto is being experimented on. Meanwhile, Naruto himself could be developing new and unexpected powers as a result of the experiments, which he then has to learn to control. And there could be a race against time for Naruto's friends to reach him before Orochimaru's experiments cause irreversible damage.