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.
In a crossover fanfiction, Goku's Ultra Instinct could lead to a crossover with the Bleach universe. He might be drawn into the Soul Society and be seen as a threat by the Soul Reapers at first. But then, they realize his power could be used to fight against the Quincy. His Ultra Instinct would give him an edge in battles against the Sternritter, and his Saiyan nature could bring a new perspective on the concept of reiatsu and spiritual power in the Bleach world.
In some fanfictions, a plot could be Goku trying to teach Ultra Instinct to his friends. Vegeta, in particular, might be a reluctant student at first but then realizes the power's potential. This could lead to a whole new dynamic among the Z - fighters, with them all striving to master this god - like ability.
Maybe Goku gets mixed up in the events of the Injustice storyline. He could initially be confused by the alternate version of Superman who has gone bad. Goku, with his pure heart and Ultra Instinct, might try to bring the corrupted Superman back to the light. This could lead to some intense battles with the Injustice League as Goku tries to set things right.
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.
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.
Another storyline could involve a character from UQ Holder learning the secrets of Ultra Instinct from Goku. This would be a great way to blend the two universes' concepts. The UQ Holder character could struggle at first to understand and master it, leading to some comical and also tense moments as they train with Goku. Maybe they have to overcome some personal limitations in order to even begin to access the power of Ultra Instinct.
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.
One possible plot development could be Goku struggling to control the Ultra Instinct state for an extended period. This might lead to him accidentally causing damage to his surroundings or even to his friends while in this super - powered state. Another could be that enemies take advantage of his 'stuck' situation, seeing it as a vulnerability to attack him when he can't fully regulate his power.
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.
Yes, it is possible. In fanfiction, writers have the creative freedom to reimagine the origin of characters. Goku being born with Ultra Instinct can add a whole new layer to his character development. It could mean that his power growth would be different from the original story, perhaps faster or with different challenges along the way.