Well, a cool Ultra Man crossover fanfiction could involve Ultra Man crossing over with the Avengers. Imagine Ultra Man showing up in the Marvel Universe and having to deal with villains like Thanos. He could use his unique powers to assist the Avengers in their battles. Also, a crossover with the Justice League would be interesting. Ultra Man could bring his own brand of heroism to the DC Universe and collaborate with Superman, Batman, and others to protect the world. A crossover with Pokémon is also a possibility. Ultra Man could help Pokémon trainers in a world where strange and powerful creatures are in danger from an unknown menace.
First, decide which two (or more) universes you want to cross. For example, if it's Ultra Man and Gundam, research both. Know their characters, powers, and storylines. Then, think of a plot that would bring them together. It could be a threat that affects both universes. Next, create an interesting character interaction. Maybe Ultra Man is initially distrusted by the Gundam pilots but they learn to work together. Finally, start writing the opening scene, setting the tone and introducing the situation.
One idea could be a crossover with the Naruto universe. Goku with his Ultra Instinct could face off against Naruto in his strongest form. They might start as rivals but then realize they have a common enemy and team up. The story could explore how their different fighting styles and powers interact.
One idea could be an Ultra Instinct Goku crossing over with the Dragon Ball Super universe and the Naruto universe. He could end up in Konoha and use his Ultra Instinct to sense and counter the attacks of the ninja there. Maybe he'd even have to fight some of the powerful ninjas like Naruto or Sasuke in a friendly sparring match to test their skills against his new form.
A possible plot is a crossover with the Naruto universe. Goku in Ultra Instinct mode could be mistaken for some sort of super - powered ninja. He might end up training with the Hokage or getting involved in the Akatsuki's plans. Since his Ultra Instinct gives him such incredible reflexes and power, he could easily hold his own against the strongest ninjas like Naruto in his Six Paths Sage Mode or Sasuke with his Rinnegan. It would be a clash of two very different power systems.
First, understand the characters well. Know Goku's Ultra Instinct powers, his personality, his goals. Then, when choosing a crossover universe, pick one that has elements that can contrast or complement Goku's world. For example, if it's a magic - based universe, how would Goku's physical powers interact with magic? Keep the story focused on the main characters and their development throughout the crossover.
First, decide which two or more universes you want to cross over. For example, if you choose Ultra Instinct from Dragon Ball and the world of Harry Potter. Then, think about how the Ultra Instinct power would work in the new universe. Would it be seen as magic? Next, create a plot. Maybe the character with Ultra Instinct has to save Hogwarts from a new dark threat. Start with a strong opening that introduces the character in the new setting.
One possible plot could be that there is a rift in the multiverse that brings Goku and Luffy together in a strange new world. They initially misunderstand each other and start to fight. As the fight progresses, they both realize that there is a greater threat at hand that is causing the rift. So, they team up, with Goku teaching Luffy some of his combat techniques and Luffy showing Goku the value of friendship and loyalty in a different way.
Well, with Ultra Instinct, Goku would be able to react extremely quickly to the DC heroes' powers. For instance, when facing Flash, who is super fast, Goku in Ultra Instinct might be able to match his speed or even anticipate his moves better. This could lead to a mutual respect between them as they test each other's limits.
Goku in Ultra Instinct mode is extremely powerful. He has superhuman speed, strength, and can dodge attacks effortlessly. However, Luffy also has his own set of amazing abilities like his Gear Fourth form which gives him enhanced speed and power. But I think Goku would win because his combat skills and power level are just on a different scale compared to Luffy.