A possible plot could be that Naruto is sent to Zero Two's world. He is initially confused by the strange mecha and the different social structure. But with his positive attitude and strong will, he befriends Zero Two and they start to understand each other's powers. Together, they could face a powerful klaxosaur that has become a threat to the entire world, with Naruto using his shadow clones and Rasengan in combination with Zero Two's franxx piloting skills.
One plot idea could be that Zero Two and Naruto are from different universes but are brought together by some sort of magical or scientific accident. They then have to team up to fight a common enemy that is threatening both of their worlds. Another idea could be that Zero Two somehow ends up in the Naruto world and has to adapt to its ninja culture while also using her unique abilities to help Naruto and his friends on a mission. Maybe she could even learn some ninja techniques herself.
One idea could be a crossover where Naruto characters gain the abilities of Megaman Zero. For example, Naruto could have Zero's saber and use it in his battles. Another idea is to set the story in a post - apocalyptic world like in Megaman Zero, but with Naruto characters trying to survive and restore peace. Maybe Sasuke could take on a role similar to Zero, being a lone warrior at first but then joining forces with others.
Another plot idea could be focusing on the backstories of the secondary characters in 'zero no tsukaima' within the fanfic. For example, we could learn more about Siesta's life before she came to the academy. It could add more depth to the overall story world and create new sub - plots.
One idea could be a crossover of Naruto's world and the Familar of Zero world where Naruto has to learn the magic system in the new world. Maybe he teams up with Saito from Familar of Zero to fight a common enemy.
Perhaps in the fanfiction, the Zero Tails is a manifestation of the negative emotions of the ninja world as a whole. A group of young ninjas discover this and they try to find a way to purify the Zero Tails. They seek the help of old sages and learn ancient jutsu to attempt this purification, which could lead to a battle against those who want to keep the Zero Tails as a weapon of mass destruction.
One idea could be exploring new ninja techniques not seen in the original Naruto series. For example, a unique combination of elemental jutsus created by a character in 'naruto ruler zero fanfiction'.
One idea could be to cross it with a modern - day world. Imagine Louise and Saito suddenly finding themselves in a bustling city. They would have to deal with technology they don't understand, like smartphones and cars. Another plot could involve a crossover with a magical school from another series. The characters could exchange magical knowledge and spells.
One idea could be exploring Aloy's life before she became the Seeker. Maybe she had a secret friendship with another outcast in her tribe. Another plot could involve a new threat emerging that is related to the old world's technology but in a way Aloy has never seen before. And perhaps a story about Aloy trying to understand the true origin of the machines beyond what she already knows.
One idea could be exploring Prisoner Zero's backstory before being imprisoned. Maybe he was wrongly accused and the oc in the fanfic could be on a quest to prove his innocence.
One plot idea could be Naruto taking Mitsuki on a special training mission in an unknown land. They encounter various new creatures and Mitsuki gets to learn unique jutsu from Naruto's experiences. Another could be a story where Mitsuki gets into trouble in the Hidden Leaf village and Naruto has to defend him, showing their bond. And they could also go on a journey to discover Mitsuki's true origins together.
Maybe a plot where Tatsuki discovers Naruto's secret about the Nine - Tails. She could initially be afraid but then come to understand him better. They then form a stronger bond as they train together to help Naruto better control the Nine - Tails' power. This could involve Tatsuki using her own training methods to assist Naruto, leading to some character growth for both of them.