One possible plotline could be that Naruto discovers a new jutsu that not only enhances his power but also changes his appearance. This jutsu might have some unforeseen side effects that gradually make him more and more handsome. For example, it could be related to chakra control and as he masters it better, his physical features start to change in a more appealing way. Maybe his hair becomes shinier, his eyes more piercing, and his face more chiseled.
In a fanfic, Naruto could be sent on a special mission to a hidden village where they have a unique beauty ritual. As he participates in it, perhaps to gain the trust of the villagers or to unlock a hidden power, he undergoes a transformation. This transformation could be both internal and external, making him more handsome as he gains new confidence and skills. He might come back to Konoha looking completely different, causing a stir among his friends and foes alike.
One possibility could be that Naruto starts taking better care of himself. Maybe he learns some new jutsu that has an unexpected side effect of enhancing his appearance. For example, a jutsu that purifies his chakra more effectively also clears up his skin and gives him a healthy glow.
A possible plotline is that a powerful villain threatens both Naruto's world and Alita's world. They are brought together by a mysterious force to stop this villain. Along the way, they face many challenges as they try to understand each other's powers and cultures. For example, Alita may not understand the concept of ninjutsu at first, and Naruto may be baffled by her mechanical body.
One possible plotline could be Naruto ending up in Alois' world and having to adapt to its different rules and power dynamics. He might use his ninja skills in unexpected ways to survive and make a name for himself.
A plotline could involve Islamic mythology or figures somehow making their way into the Naruto universe. Maybe an Islamic - inspired spirit or entity appears in the Hidden Leaf Village and has to be dealt with, and the characters learn about Islamic beliefs in the process.
A plotline for a Naruto Keyblade fanfic could start with Naruto finding a strange Keyblade - like object during one of his missions. As he tries to figure out what it is, he accidentally activates it and is sent to a different realm. In this realm, he meets other Keyblade wielders who help him understand the power of the Keyblade. Meanwhile, back in the Naruto world, his friends are worried about his disappearance and start searching for him. Naruto then has to master the Keyblade and find a way back home while also dealing with any threats in the new world.
A possible plotline could be Naruto and his friends being transported to the WW2 era. They then use their ninja skills to try and stop the war. Or perhaps they side with one of the Allied forces and help them in their battles. Another plotline could be that a powerful Naruto villain teams up with a WW2 dictator and they create chaos together. The heroes have to then find a way to defeat this unholy alliance.
One possible plotline could be that Naruto is exposed to a dark and powerful jutsu that gradually transforms him into a monster. He might start to lose his sense of self and his friends have to find a way to reverse the process. For example, Sasuke could use his Sharingan to try and understand the nature of the transformation and look for a weakness in the dark jutsu.
One possible plotline could be that Naruto is cursed by a powerful dark jutsu during a battle. This jutsu slowly transforms him into a demon. As he changes, his friends initially try to find a way to reverse it. But Naruto starts to gain new powers that he must learn to control, and he has to struggle between his human side and the emerging demon nature.
Another plotline could involve Naruto being chosen by some ancient and powerful force to become a god. As a god, he has to deal with other divine beings. He may face challenges like jealousy from other gods or having to prove himself worthy in the divine realm while still caring about his friends and the village he left behind.
One possible plotline could be Naruto being exposed to some sort of dark jutsu that warps his mind and makes him idolize Tobi. He might start to adopt Tobi's methods and goals, causing chaos in the ninja world. His friends would be shocked and try to bring him back to his senses.