One idea could be that Naruto is on a mission in a new land and he meets Ahri. Ahri is initially suspicious of Naruto but as they face some common enemies together, they start to trust each other. Another plot could be that Ahri somehow gets transported to the Naruto world and Naruto has to help her get back home while also protecting her from those who might want to use her powers.
A really interesting plot could be set in a post - war Naruto world. Ahri arrives there, perhaps by accident. Naruto, now a respected leader, has to deal with the presence of this strange new being. At first, there are misunderstandings and some of the villagers are afraid of Ahri. But Naruto sees her good side. As they interact more, they discover that they both have a longing for peace and understanding in their respective worlds. They then team up to try and create a better world for all, combining Ahri's magic and Naruto's ninja skills.
Well, a possible plot is that the male reader is a warrior who has been injured near Ahri's territory. Ahri, with her kind heart, decides to nurse him back to health. As he recovers, they start to communicate through gestures and simple words. Their relationship deepens as they face threats from other creatures in the forest together. Also, perhaps the male reader is a scholar researching magical creatures and Ahri becomes his main subject of study. But as he gets to know her better, their relationship turns from just research to something more romantic.
Perhaps the summoner gets lost in a dangerous part of the League of Legends world, and Ahri, being the curious and kind - hearted fox spirit she is, decides to rescue the summoner. Along the way, they develop a deep bond and learn more about each other's pasts.
In some Naruto and Ahri fanfiction, they could be on a journey together to discover a powerful and ancient artifact. Along the way, they meet different characters from both their worlds. Ahri's intelligence and Naruto's determination would make them a great team. They would face many challenges like solving puzzles, fighting off other powerful beings who also want the artifact, and learning to trust each other completely.
A plot could revolve around Sesshomaru being intrigued by Naruto's determination. Sesshomaru decides to train Naruto in some of his own combat techniques, which Naruto adapts to his own fighting style. In return, Naruto shows Sesshomaru the value of friendship and loyalty within a village. This could lead to Sesshomaru having a change of heart about his own solitary ways. Also, they could team up to face a common foe from Sesshomaru's world that has somehow entered the Naruto universe.
One idea could be that Naruto and Kashuina meet during a mission outside of Konoha. They start off as rivals, constantly trying to outdo each other in combat skills. But as they face various challenges together, they gradually develop a mutual respect and then deeper feelings. Another plot could be set in a post - war scenario where Naruto, now a hero, meets Kashuina who has a unique ability to heal the psychological scars of the war - torn ninjas. Their interaction then leads to a romantic relationship. And a third idea is that they are both students under a new sensei who pairs them up for special training. During this training, they discover things about each other that they never knew before and fall in love.
One idea could be Naruto being sent to the world of Death Note. He could use his ninja skills to try and outwit Light Yagami. Maybe he would initially be confused by the Death Note's power but then use his determination to stop Light from his killing spree. Another plot could involve Naruto meeting the Shinigami. He might learn about the balance between life and death in this new context and try to find a way to bring some of his ninja world's values to this strange new world.
Perhaps Naruto and Lala meet during a mission where Naruto is sent to a different dimension. Lala, being from an alien world, is intrigued by Naruto's determination and they form an alliance to face a common enemy in that dimension. Their different powers and abilities complement each other, and as they work together, they start to develop feelings for each other.
A more complex plot could be that there is a prophecy in both worlds about a union between someone from the Naruto universe and someone from Ruby's universe. Naruto and Ruby are the ones fated to fulfill this prophecy. They initially don't get along but as they face various challenges together, they start to understand each other and fall in love, while also saving both their worlds in the process.
In a naruto x avatar fanfiction, there could be a scenario where the Akatsuki from Naruto's world teams up with some of the villains from the Avatar world. This would force Naruto and the Avatar (whichever one it may be) to put aside their differences and form an alliance with other characters from both worlds to stop this powerful and evil coalition.
One idea could be that a zombie virus spreads in the Naruto world. Naruto and his friends have to not only fight the zombies but also figure out how the virus started. Maybe Orochimaru was experimenting with dark jutsu and it went wrong.