Well, a great plot could be centered around the concept of chakra in the Heroic Age. Imagine if Naruto's chakra was seen as a new form of power in that world. The characters from the Heroic Age might try to either harness it or destroy it out of fear. Also, a crossover could explore how the ninjas' stealth and combat skills compare to the fighting styles in the Heroic Age.
One idea could be to explore the backstories of minor characters during the Heroic Age. For example, how did some of the ninja who weren't in the main spotlight contribute to the overall development of the Hidden Villages? Another idea is to create an alternate timeline where different alliances were formed during the Heroic Age. This could lead to completely different power dynamics and storylines. Maybe a group of outcast ninjas form their own village and have to fight for recognition.
Well, in 'heroic age crossover fanfiction', the exploration of different cultures within the crossovers is really cool. Imagine a story where the values and traditions of the heroic age are juxtaposed with those of a completely alien culture from another fictional realm. It can lead to some really thought - provoking scenarios and character development.
One idea could be a crossover with 'The Lion King'. The Ice Age characters could end up in the Pride Lands. Sid might make friends with Timon and Pumbaa, while Manny and Diego have to deal with the lions. Another could be a crossover with 'Finding Nemo'. The Ice Age gang could somehow find themselves in the ocean, trying to help Marlin find Nemo. It would be a really wacky and fun adventure.
One idea could be to cross the Ice Age world with a fantasy world. Have the Ice Age characters encounter magical creatures like unicorns or dragons. Another could be a crossover with a modern - day world, where the prehistoric animals have to adapt to the strange new environment full of skyscrapers and cars.
For 'Age of Ultron Crossover Fanfiction', a crossover with the DC universe would be epic. Superman and the Avengers could join forces to take on a greater threat that combines the villains from both universes. Or, a crossover with the Transformers. The Avengers could work together with the Autobots to stop Ultron from getting his hands on the powerful technology of the Transformers. This would lead to some amazing battles and team - up moments.
One interesting plot idea could be a crossover where Naruto's senjutsu abilities are combined with another universe's magic system. For example, if he were to cross over into the Harry Potter universe, he could use senjutsu to enhance his magic or even teach the wizards about chakra. Another idea is a crossover with the Dragon Ball universe, where Naruto's senjutsu clashes with the ki energy of the Saiyans. Maybe he has to use senjutsu to face off against a powerful Saiyan who has come to the Naruto world. Or a crossover with the Bleach universe, and Naruto uses senjutsu to interact with the spiritual energy there, perhaps even helping Ichigo in a battle against a powerful Hollow by using his unique senjutsu skills.
One plot idea could be that Naruto characters end up in Ikebukuro. For example, Naruto himself could be searching for a new type of ninja tool that he heard can only be found in Ikebukuro. Meanwhile, the gangs in Durarara start to notice this strange, orange - clad boy with strange powers. Another idea is a character swap where some of the Durarara characters gain ninja abilities and get involved in Naruto - style battles in their own world. Maybe Celty could use her shadow powers in a more ninja - like way, like stealth and quick attacks.
One idea could be that Naruto characters are transported into the Splatoon world. They might initially be confused by the ink-based battles and the unique species. For example, Naruto could mistake an Inkling for a strange ninja from another land and challenge them to a friendly spar, only to find out about the ink shooting mechanism. Another plot could involve the Akatsuki from Naruto trying to steal the valuable ink resources in the Splatoon world for their own purposes. They would face off against the Splatoon heroes who are determined to protect their world's resources.
A cool plot could be that there's a tournament across different anime worlds, and Inuyasha and Naruto are chosen to represent their respective worlds. Along the way, they discover similarities in their pasts, like both having some form of demon - related heritage (Naruto with the Nine - Tails and Inuyasha being a half - demon). They also exchange combat techniques. Naruto teaches Inuyasha how to better use chakra control in his attacks, and Inuyasha shows Naruto some unique sword - fighting skills.
One interesting plot idea could be that Kaguya is reborn in the modern Naruto world. She has no memories of her past at first. Naruto discovers her and senses a strange power within her. As she starts to regain her memories, she struggles between her old self and the new world she's in. Naruto has to decide whether to trust her or not.