Well, perhaps there's a magical object in the Charmed universe that is the key to unlocking a new power within Naruto. And in return, Naruto has to help the Charmed ones protect this object from a group of rogue ninjas who have also found their way into the Charmed world. The ninjas want to use the object to gain ultimate power over both worlds. Naruto could teach the sisters some ninja techniques like stealth and hand - to - hand combat while they help him understand and control the new power with their magical knowledge.
A great plot might be that there is a prophecy in both the Naruto world and the Charmed world. In the Naruto world, it's about a foreign land that will bring either great chaos or great harmony, and in the Charmed world, it's about a strange visitor who will either save or destroy them. Naruto turns out to be this visitor. He has to work with the Charmed sisters to figure out if they can fulfill the positive side of both prophecies. Along the way, they face challenges like dealing with the prejudiced witches who don't trust Naruto at first, and Naruto has to adjust to the new magical rules and society of the Charmed world.
Perhaps a spell gone wrong in the Charmed universe causes a portal to open to the Twilight world. The Charmed Ones end up in Forks and meet the Cullens. They initially suspect the Cullens of being dark magic users but then realize they are vampires. Together they face a common enemy that is drawn to the combined magic and vampire allure in the area.
One idea could be that the Charmed Ones and Buffy team up to fight a powerful demon that has the ability to move between their two worlds. They have to combine their unique magical powers and slaying skills to defeat it.
One idea could be that the Charmed Ones have to team up with the Winchesters to stop a powerful demon that is causing chaos in both their worlds. Maybe the demon has a spell that can break the magical protections of the Halliwell Manor and is also targeting hunters. Another could be a crossover where Phoebe's premonition power combines with Sam's psychic abilities to foresee a major apocalypse event that they must prevent together.
One idea could be that the Halliwell sisters somehow end up in Camelot. They could use their magic to help Merlin deal with a powerful dark sorcerer that even his magic can't handle alone. Maybe they teach him some new spells or ways to control his magic better.
Well, perhaps in this fanfiction, the SAO system is corrupted by an Orochimaru - like figure. He wants to use the virtual world to gain power and immortality. Naruto and his friends, along with the SAO players, have to team up. Naruto's positive attitude and never - give - up spirit inspire the SAO players. They all work together to defeat this new threat, with Naruto using his Rasengan in new and creative ways within the SAO world.
A plot could involve the Killzone characters getting access to chakra. Some of the Killzone soldiers might start to learn ninjutsu and this causes chaos in their own military structure. Meanwhile, Naruto has to figure out how to get back to his own world while also dealing with the new threats that this crossover has created. Maybe he teams up with some of the more honorable Killzone soldiers to find a solution.
A plot might involve Naruto being sent to Bayonetta's world. He'd be out of his element, but his determination would shine through. Bayonetta could mistake him for a strange demon at first. However, they soon realize they can help each other. Naruto's chakra could interact in unexpected ways with Bayonetta's magic. Together, they could face off against Bayonetta's foes, like the angels, with Naruto's Rasengan combined with Bayonetta's Witch Time abilities making for some epic battles.
In a Naruto and Spiderman crossover, it could start with Spiderman noticing some strange energy signatures in his city. These turn out to be Naruto's chakra flares. Naruto is there looking for a way back to his own world after being accidentally sent to Earth - 616 (the Marvel Universe). They meet and at first don't understand each other. However, when they see a common enemy, a group of ninjas - like mutants who are causing chaos, they decide to work together. Spiderman uses his agility and web - shooting while Naruto uses his jutsu to defeat the bad guys.
One possible plot could be that Naruto and his team are on a mission in a strange new land that turns out to be the world of Claymore. They encounter Claymores, the half - human, half - yoma warriors. Naruto, with his never - give - up attitude, tries to understand the complex relationship between humans and yoma in this world. He could end up befriending some of the Claymores and together they fight against a powerful common enemy that threatens both their worlds.
One possible plot could be that Naruto, while on a mission, somehow gets transported to the world of Undertale. He teams up with Frisk to stop Flowey from taking over both their worlds. Naruto's ninja skills, like his shadow clones, could be used in creative ways in the battles against the monsters in Undertale.