Perhaps the Rinnegan is the key to understanding the origin of the zombie virus in the high school. A character with Rinnegan starts having visions of the past that show how the virus was created, maybe by a rogue ninja from Naruto's world who was experimenting with dark jutsu. The survivors then have to use the various abilities of the Rinnegan, like the Animal Path to summon creatures to help them fight the zombies, while also trying to find a way to reverse the virus. This would involve a lot of exploration within the high school, which could be filled with all sorts of zombie - related threats and hidden secrets related to the Rinnegan.
A plot idea could be that a group of students suddenly develop Rinnegan powers during a zombie outbreak in their high school. They must then figure out how to use these powers to not only survive but also find a cure. Another idea is that a Naruto - like character from another dimension arrives in the Highschool of the Dead world with Rinnegan and tries to teach the survivors ninjutsu to fight the zombies.
One idea could be a crossover where Naruto characters are suddenly thrown into the Highschool of the Dead world. They could use their ninja skills to fight off the zombies. For example, Naruto could use his shadow clones to distract the zombies while others find a safe place. Another plot could involve a Highschool of the Dead character getting ninjutsu powers and having to learn to control them like a Naruto character. Maybe they accidentally use a fire - style jutsu in the middle of the school, causing chaos among the survivors and the zombies.
One idea could be that Naruto's immortality gives him unique abilities in the high - school - during - the - zombie - apocalypse setting. For example, he could use his shadow clones to distract the zombies while he and his friends find a safe haven. Another plot idea might be that Naruto discovers a way to cure the zombie virus using his chakra, but he has to face many challenges and enemies who want to use the cure for their own evil purposes.
One idea could be to explore the backstories of the minor characters in more depth. For example, the story could focus on a side character's journey before the zombie apocalypse and how they've changed since then. Another plot could be a survival story that takes place in a different location than the original, like an isolated island where they have to deal with not only zombies but also limited resources.
Well, a cool plot for a Rinnegan Naruto crossover fanfiction could be that there is a rift between the Naruto world and a world where the Rinnegan is more common. Naruto gets pulled into this other world and has to adapt to the different power system there. He meets characters who have mastered the Rinnegan and has to learn from them to find his way back home. Along the way, he discovers a connection between the two worlds that was hidden for centuries.
One plot idea could be a story where Naruto discovers he has the Mokuton and Rinnegan abilities due to some ancient curse or prophecy. He then has to learn to control these new powers while facing off against a new, powerful enemy that is immune to normal jutsu. Another idea is a fanfic where Naruto uses his Mokuton and Rinnegan to travel to different dimensions to find a way to save the Hidden Leaf from a looming disaster. Or perhaps a story where he has to team up with old enemies who are also intrigued by his new powers and together they form an uneasy alliance to fight a greater evil.
One interesting plot could be a character with the red rinnegan having the power to manipulate time on a small scale. For example, they can rewind a few seconds during a battle to avoid an attack or foresee an enemy's move. Another idea is that the red rinnegan gives the ability to communicate with ancient spirits of the Naruto world, which could lead to uncovering long - lost secrets about the origin of chakra.
One plot idea could be that Naruto and Sasuke discover a new power related to the Rinnegan that can only be accessed when they combine their chakra. Another could be a time - travel plot where they go back in time to prevent the creation of the Rinnegan in the wrong hands. Maybe they have to face an enemy who has a corrupted version of the Rinnegan powers and they must use their own understanding of the power to defeat them.
Perhaps a plot where Naruto's Rinnegan is a result of a curse placed on him by an ancient evil. As Hokage, he has to not only fight against external threats but also the inner struggle of controlling the power of the Rinnegan without succumbing to the curse. He could learn about the origin of the Rinnegan from old scrolls and seek the help of sage-like characters to overcome the curse.
One idea could be a story where Naruto and Sasuke are rivals in high school sports. They compete in track and field events, with Naruto's determination against Sasuke's natural talent. Another could be about Hinata being the shy new girl in school and Naruto slowly befriending her and helping her come out of her shell. Maybe there's a high school ninja club where they all learn and practice ninjutsu in a modern setting.
One interesting plot idea could be a pre - apocalypse story within the Highschool of the Dead universe. Maybe showing how the relationships between the main characters were developing before the zombies showed up. For example, Rei and Takashi's friendship turning into something more complex as they dealt with normal high school drama.