A more comical plot could be Ultraman Orb crossing over with a group of clumsy but well - intentioned superhero wannabes. He has to train them up while also dealing with the real threats that start to emerge. This would bring in some humor as he tries to get them in shape while also saving the day.
A cool plot could be Geed crossing over with a human superhero from another franchise. For example, he meets a spandex - clad hero who has no experience with giant monsters. Geed has to teach this hero how to fight in a world where the threats are so much bigger, and together they face a villain who has the ability to control both technology and kaiju.
One idea could be Ultraman Nexus crossing over with another Ultraman, like Ultraman Tiga. They could team up to fight a powerful new enemy that is a combination of their previous foes. This would bring together different fighting styles and powers.
Another plot could involve Ultraman Zero crossing over to a post - apocalyptic Earth. He finds a group of survivors who are fighting against mutated monsters. Zero has to use his powers not only to defeat the monsters but also to help the survivors rebuild their society, teaching them about hope and perseverance.
One idea could be an Ultraman crossover with Godzilla. Picture Ultraman teaming up with the giant lizard to fight a common enemy, like an alien kaiju that's too powerful for either of them alone. It would be epic to see their different powers combine, for example, Ultraman's energy beams along with Godzilla's atomic breath.
Definitely Ultraman Zero. He's a very popular Ultraman and his skills and personality would make for an interesting combination with Ultraman Orb. They could have some friendly rivalries while fighting side by side against a common foe.
One idea could be that the time travel orb sends Naruto to a crucial point in the past where he can prevent a major tragedy. For example, he might be able to stop the Uchiha massacre, which would change the entire future of the ninja world. This would lead to different alliances and power dynamics.
One idea could be that the reader is a scientist who accidentally discovers a new power source that attracts Ultraman Zero. They then team up to protect it from evil forces. Another could be the reader is from a different dimension and Ultraman Zero has to help them get back home while facing various challenges together.
Maybe a crossover with a magical anime. The nanbaka characters could suddenly find themselves in a world full of magic. Some of the nanbaka characters might be really good at using magic in unexpected ways, like Jyugo using his shackles in a magical battle.
A crossover with a modern - day action story could be really cool too. Spartacus and his crew could be brought to the present day through some time - travel mishap. They then have to navigate the modern world, learning about new weapons and technology. They could use their ancient fighting techniques in modern combat situations, like taking on a powerful criminal organization.
Maybe in the fanfiction, the three - tailed beast crosses over into a modern - day human world. People initially fear it, but then they discover that it has a gentle side and is actually trying to find its way back home. It could form a bond with a group of humans who help it on its journey, leading to many adventures along the way.