One possible plot could be that Naruto discovers he has some devilish powers due to an ancient curse. He has to learn to control these powers while still maintaining his ninja way. He could face discrimination from his village at first, but then use his new powers to protect them from a powerful new enemy that normal ninja techniques can't defeat.
A good plot might be that a powerful devil from another realm is interested in Naruto's chakra. This devil makes a deal with Naruto, offering him enhanced power in exchange for some of his chakra. Naruto, being naive at first, accepts. But then he realizes the devil has malicious intentions. He has to fight against the devil's influence while also using the new powers he's gained in a way that doesn't corrupt him, all while trying to keep it a secret from his friends in Konoha.
A new character could be a half - devil, half - ninja girl. She has the allure of the devil with the stealth of a ninja. She could be initially an antagonist, trying to steal Naruto's newfound devil powers, but later becomes an ally. Another character could be an old devil sage who teaches Naruto about his devil heritage and how to use his powers properly.
In this kind of fanfic, it might be that a group of rogue ninjas obtain devil breakers and start causing chaos in the ninja world. Naruto, being the hero he is, decides to study these devil breakers to find their weaknesses. He meets an old hermit who has some knowledge about them. Along the way, Naruto also has to deal with his friends' doubts about using such foreign and potentially dangerous technology. He has to prove that he can use it for good and stop the rogues before they destroy everything he holds dear.
In a 'Naruto is a Phoenix Devil' fanfic, the plot could involve Naruto being transformed into a Phoenix Devil through some kind of magical or cursed event. This new form could bring internal struggles as he tries to control the devilish instincts while still holding onto his ninja values. He might also have to face off against other powerful entities in the ninja world who see his new power as a threat.
The plot could involve a quest. Maybe a powerful artifact from the Naruto world has ended up in Monster High, or vice versa. Naruto and his friends have to travel to Monster High to retrieve it. Along the way, they face challenges like dealing with the school's spooky environment and making friends with the Monster High students.
One possible plot could be a story where Naruto gets seriously injured during a battle and is taken to the hospital. There, he meets a young and talented medic - ninja who has a unique healing ability. As he recovers, they form a bond and the medic - ninja helps Naruto discover a new way to control his chakra, which in turn helps him become stronger.
One possible plot could be that Naruto is on a mission in a new land and he meets Sheeva. Sheeva is from a tribe with unique powers and Naruto has to team up with her to defeat a common enemy that threatens both their worlds. They start off not getting along well because of their different cultures and ways of doing things, but as they face challenges together, they learn to respect each other and combine their powers in a creative way to win the battle.
One possible plot could be that Naruto, in his devil form, meets Serafall in the underworld. They start off as rivals, constantly competing in various devilish tasks or battles. But as time goes on, they begin to see the good in each other. Naruto's strong sense of justice and loyalty, which he carried from his shinobi days, intrigues Serafall. And Serafall's charm and power attract Naruto. Eventually, they fall in love and get married, uniting the power of the shinobi world and the devil world in a unique way.
One possible plot could be that Naruto is the popular but a bit of a troublemaker in high school. Hinata is the shy girl who has a huge crush on him. They get paired up for a school project and Naruto starts to see Hinata in a new light as she shows her intelligence and kindness during the project.
One possible plot could be that Brennan and Booth reunite at their high school reunion. They see how much each other has changed and yet how some of their old chemistry is still there. They start reminiscing about their high school days and realize they had some unspoken feelings back then. As they catch up on their current lives, they begin to wonder if they could have a future together.
One possible plot could be a new student joining the climbing class. They are initially shy and intimidated by the more experienced climbers. But with the help of a friendly and skilled classmate, they start to improve and gain confidence. Eventually, they both participate in a big climbing competition together.