One possible plot could be that a powerful necromancer from the Naruto world accidentally unleashes a zombie plague. Naruto and his friends have to not only fight their zombified comrades but also find a way to reverse the spell. They could use their ninja skills in unique ways, like using shadow clones to distract the zombies while they search for a cure.
I'm not sure if there is an exact fanfiction titled 'naruto is this a zombie crossover fanfiction'. There are countless fanfictions out there, and it could exist, but without searching specific fanfiction platforms, it's hard to say for certain.
Sasuke could be really engaging in this scenario. His cold and calculating nature would be a contrast to the chaos of the zombies. He might see the zombie outbreak as an opportunity to gain more power or find a way to use the situation to his advantage against his enemies in the Naruto world. And his Sharingan could potentially have some new abilities when dealing with the undead.
One idea could be that Bella, instead of becoming a vampire, is bitten by a zombie. She then has to struggle with her new zombie nature while still holding onto her humanity. For example, she might try to resist the urge to attack her human friends like Jacob and Charlie.
One possible plot could be that Naruto has to go on a special mission with Kurenai. They might be sent to a hidden village where they discover a new type of jutsu that is being misused. Kurenai's genjutsu skills and Naruto's rasengan could be combined in unique ways to fight against the villains using this jutsu.
One possible plot could be that Riddick somehow gets transported to the Naruto universe. He could initially be seen as a threat, but then he teams up with Naruto and the others to fight a common enemy, like a new powerful Akatsuki member who has powers similar to some of the creatures in Riddick's world. Riddick's combat skills and his ability to see in the dark could give the Naruto gang an edge in battles.
One interesting plot could be that Naruto and The Flash team up to stop a villain who can manipulate time. The Flash uses his speed to move between different time periods while Naruto uses his shadow clones to gather information across a large area. They would have to learn to combine their powers and trust each other's instincts in order to succeed.
Well, perhaps in this crossover, Sephiroth is a rogue ninja from a far - off land that has powers similar to his in the Final Fantasy world. He starts causing destruction in the Hidden Leaf Village. Naruto, being the hero, decides to face him. Along the way, they discover that their powers have some strange similarities. For example, Sephiroth's sword techniques could be compared to some of the advanced sword - using ninja in the Naruto world. And they might end up having to team up against a greater evil that emerges because of Sephiroth's arrival.
One possible plot could be that Lucifer, bored with the underworld, decides to visit the Naruto universe. He could take on the form of a powerful ninja and start causing chaos, which draws the attention of Naruto and his friends. Naruto, seeing the evil in Lucifer's actions, tries to convince him to change his ways, leading to a series of battles and philosophical debates.
A cool plot could be that there is a prophecy in both the Naruto and Percy Jackson worlds. It predicts the coming together of a shinobi and a demigod to save both realms from a powerful, interdimensional evil. Percy arrives in the Naruto world, and he and Naruto have to learn each other's skills. Percy teaches Naruto about Greek mythology and how to fight mythical creatures, while Naruto shows Percy the ways of chakra and ninjutsu. They then journey to different parts of the Naruto world, gathering allies and knowledge to face the impending doom.
One possible plot could be that Naruto, while on a strange mission, gets transported to the Witcher's world. He teams up with Geralt to hunt a powerful demon that has the ability to control minds. Naruto's unique ninja skills, like his shadow clones, would be very useful in distracting the demon while Geralt figures out its weakness.