A possible fanfiction could be about a character from Naruto being summoned to the world of Smite by Hel. She could have an ulterior motive, like using Naruto's chakra for her own dark purposes. Naruto, not understanding the new world at first, has to quickly adapt and use his skills to either escape Hel's clutches or find a way to work with her to solve a greater problem that affects both his world and the Smite world.
In a Naruto and Hel Smite fanfiction, it could be set in a scenario where the power balance in the Smite world is disrupted. Hel, seeing Naruto's power from another dimension, decides to make a deal with him. Naruto, being the hero he is, is hesitant but realizes that by working with Hel, he might be able to save both his world and the Smite world from an impending doom that is slowly spreading across both realms.
To write a good fanfiction, do a lot of research on the Naruto universe and the Smite game. For the Naruto part, study the different jutsus, the relationships between characters, and the overall theme of friendship and growth. In Smite, understand the mechanics, the gods, and how Hel fits into the game world. Then, start with a strong hook, like Naruto suddenly appearing in the Smite world and being confronted by Hel. Develop the story from there, making sure to keep the characters' personalities true to their original sources.
A cool Naruto and Smite fanfiction idea could be a time - travel story. A Naruto character, like Sasuke, travels to the Smite world and has to learn the ways of the gods to get back home. He could form alliances with certain gods based on their similar personalities or powers. For instance, he might team up with Loki because of their shared penchant for trickery. Another concept could be a story where the Nine - Tailed Fox in Naruto is actually related to a powerful beast in the Smite world, and this connection causes all sorts of chaos and revelations in both universes.
Another concept is that Naruto is sent to Middle - earth. There, he could use his ninja skills and chakra powers. He and Gandalf could team up to fight Sauron. Naruto's ability to make friends and inspire others would be really useful in uniting the different races of Middle - earth against the common enemy.
One idea could be a crossover where Naruto characters gain the abilities of Needless characters. For example, Naruto could get the power of Adam Blade's regeneration. It would be interesting to see how he uses it in battle, especially against tough foes like Pain or Madara.
Another fanfiction concept could be that a few ninjas, including Naruto, are given the ability to transform into mini - Transformers. They could use these new forms to gain an edge in battle, combining their ninja skills with the advanced weaponry and abilities of the Transformers. This would create a whole new dynamic in the Naruto battles and introduce some really interesting fight scenes.
Another concept is that Euphemia discovers a strange portal and steps through it, ending up in the Naruto universe. There, she befriends Naruto and his friends. She could use her diplomatic skills to try and bring peace between the warring ninja clans, while also learning some ninja techniques herself.
One idea could be to have Naruto enter the world of Bloodborne. Maybe he is on a mission and accidentally gets transported there. He would have to deal with the dark and dangerous creatures using his ninja skills. His chakra could be an interesting element in this world, perhaps being mistaken for some sort of otherworldly power by the inhabitants of Bloodborne.
Maybe Naruto discovers Cortana's existence while on a mission in a strange dimension. He is intrigued by her digital form and her ability to store vast amounts of information. Cortana, in turn, is fascinated by Naruto's determination and the concept of chakra. They form an unlikely alliance to face new threats that are emerging in both their worlds.
Another fanfiction concept could be that Hachishakusama is somehow summoned into the Naruto world during a battle. Naruto and his friends initially think it's an enemy but then realize it's a being from another dimension. They have to figure out a way to send it back, perhaps by using some ancient sealing jutsu that Naruto has to learn specifically for this task.
Another possibility is that Godzilla somehow ends up in the Naruto world. The shinobi might initially see it as a great threat, but Naruto could try to communicate with it using his ability to sense emotions. Maybe Godzilla is there because it's being chased by an even greater enemy from its own world, and Naruto and his friends decide to help it.