One idea could be Naruto discovers a hidden realm where devil hunters operate and he has to learn their ways to save his village from a devil invasion.
One idea could be that Naruto and Gon meet during a strange interdimensional rift. They initially misunderstand each other but soon realize they have a common goal of protecting their friends and worlds. Another could be that the Akatsuki and the Phantom Troupe somehow cross paths and form an uneasy alliance to achieve their own ends, which involves stealing powerful artifacts from both Naruto's world and the Hunter x Hunter world. And a third idea might be that Naruto and Killua swap places for a short time, experiencing the different power systems and cultures of each other's worlds.
One interesting plot idea could be a crossover where Naruto characters enter the Hunter x Hunter world and have to adapt to its unique nen abilities. For example, Naruto might try to use his chakra in new ways to mimic nen techniques.
One idea could be a crossover where an Ice Devil Slayer from another dimension arrives in the Naruto world. They could team up with Naruto to fight against a new ice - based enemy that is freezing the land. This would bring a new element of magic to the Naruto universe.
Perhaps the Devil's Advocate could be a figure from Naruto's past who returns with a new, more devious ideology. They could tempt Naruto to abandon his traditional values of friendship and hard work in favor of a quicker, more self - serving path to power. This could create an internal struggle within Naruto as he battles between his old beliefs and this new, tempting but dangerous perspective.
Well, a plot might involve a devil approaching a young and inexperienced Hunter. The devil offers the Hunter a deal to become the most powerful Hunter ever in return for the Hunter's soul after a certain period. As the Hunter rises in power, they attract the attention of other Hunters, some who suspect something is wrong. This could lead to a conflict between those who want to help the Hunter break the deal and those who see the Hunter as a threat due to their newfound and possibly dangerous power. Also, the devil could be using the Hunter to start chaos in the Hunter x Hunter world for its own mysterious reasons.
One idea could be that Naruto discovers his half - angel half - devil heritage during a dangerous mission. Maybe he starts to have new powers like the ability to heal rapidly (angel side) and also to unleash dark energy (devil side) which he has to learn to control.
A possible plot could be that the devil fruit that Shiki has is a Logia - type devil fruit which allows him to turn into a certain substance. In the Naruto world, this confounds Naruto and his friends as they've never faced such an ability before. Shiki uses this power to infiltrate villages undetected. Naruto starts to study the nature of the devil fruit's power with the help of some of the more knowledgeable characters in the series, like Jiraiya (if he's still alive in this fanfiction). They eventually find a weakness in Shiki's power, which lies in a certain type of chakra that can disrupt the devil fruit's transformation process.
Another interesting plot could involve a magic - based tournament where characters from both Naruto and The Devil is a Part - Timer participate. Naruto's ninja skills and chakra - based abilities would be pitted against the magic of the characters in The Devil is a Part - Timer. It could lead to some unique battles and alliances.
A third plot idea is that the Devil May Cry crew visits the Naruto world. Yamato is tasked with training them in ninja skills. But they soon find out that there are dark forces at work in the Naruto world that are related to the demons they fight in their own universe. Together, they must figure out how to stop these forces.
One idea could be a character with a devil bloodline being initially shunned in the Hidden Leaf Village but then proving their worth in a major battle. For example, they could use their unique devil - like abilities, such as enhanced speed and strength, to turn the tide against a powerful enemy.