One idea could be Naruto being dropped into the Fallout wasteland. He might use his ninja skills to survive, like his stealth and agility to avoid mutants. His Rasengan could be a powerful weapon against raiders.
Another interesting concept is that Naruto's shadow clones could be used in unique ways in the Fallout setting. For example, he could send clones to explore dangerous areas or distract enemies while he goes for the main objective. And his ability to endure hardships in his own world would make him a formidable survivor in the post - apocalyptic Fallout world.
Perhaps in this fanfiction, the chakra in Naruto's world is related to the radiation in Fallout. He could learn to control the mutated energy in the wasteland as if it were chakra. And he might team up with some of the Fallout characters to fight against the big bads, like the Enclave.
A more complex plot might be that Naruto's presence in the Fallout 4 world starts to change the balance of power. His positive energy and strong will begin to inspire the people in Piper's settlement. Meanwhile, Piper helps Naruto understand the political and social dynamics of the wasteland, and together they try to bring peace and unity among the different factions.
How about the idea of the ninjas from Naruto trying to find a way to reverse the radiation in Fallout 4? They could use their chakra knowledge and skills. Hinata could use her byakugan to detect sources of radiation more accurately. And Naruto could use his positive energy and willpower, which is often associated with his chakra, to try and purify some of the polluted areas.
One idea could be an OC who is a brilliant scientist in the Fallout world. They could be working on a secret project to reverse the effects of radiation. Another idea is an OC who is a wandering trader, having all kinds of adventures while traveling from one settlement to another, facing raiders and mutants along the way. And a third idea could be an OC that is part of a new faction trying to bring peace and order to the wasteland.
One idea could be a character from the Enclave finding themselves in a situation where they have to team up with a group from the Fallout world they usually oppose. Maybe a lone Enclave soldier gets separated from his unit and is forced to rely on a group of wastelanders to survive. This could lead to a lot of character development as he sees a different side of the world outside the Enclave's ideology.
One idea could be a crossover where characters from Fallout enter the RWBY universe. For example, a Vault Dweller could end up in Vale and have to adapt to the Grimm - filled world while also trying to find a way back home. Another could be a story where RWBY characters are thrown into a post - apocalyptic setting like in Fallout, dealing with radiation and mutated creatures.
One idea could be a story where the protagonist, a lone wanderer, gradually gathers a diverse group of female companions from different factions in the Fallout world. For example, a Brotherhood of Steel scribe, a raider who has a change of heart, and a super mutant with a unique personality. Their relationships could develop as they face various threats together, like fighting off hordes of feral ghouls or taking on powerful raider gangs.
One interesting idea could be the combination of Naruto's ninja skills with mecha technology. For example, Naruto might use his chakra to power up the mecha in unique ways. Another idea could be the new enemies that are created specifically for this mecha - Naruto concept, like robotic shinobi that require different combat strategies compared to normal foes. Also, the design of the mecha Naruto itself can be really cool, perhaps with features inspired by the Nine - Tails.
One interesting plot idea could be a time - travel story. For example, Naruto is sent back in time to the era of the First Hokage. He could use his knowledge of future jutsu and events to change things for the better in the past. Another idea is a story where Naruto discovers a hidden clan within Konoha that has a unique and powerful Kekkei Genkai. He then has to help this clan gain acceptance in the village. A third idea might be a story where Naruto is turned into a different creature, like a cat or a fox, and has to find a way to turn back while still dealing with the normal threats to the village.
One idea could be a story where Naruto discovers a hidden nano - technology in the Hidden Leaf Village that was left by an ancient shinobi. This tech gives him new powers to fight enemies.
One idea could be that the characters from RWBY end up in the Fallout wasteland. Ruby could use her scythe skills to fight off raiders and mutants. Weiss might use her glyphs to protect the group from radiation in certain areas. Another idea is that the Dust from RWBY could be a valuable resource in the Fallout world, leading to various power struggles.