Well, here's an idea. There's a powerful cosmic entity that's siphoning energy from both the Dragon Ball universe and the Marvel universe. Goku and Captain Marvel sense this and are drawn to the source. Along the way, they meet various allies and enemies from both universes. They start to teach each other their unique combat techniques. Goku shows Captain Marvel the Kaioken and Spirit Bomb, while Captain Marvel teaches Goku about her energy projection and flight skills. As they get closer to the entity, they face tougher challenges and have to trust each other completely to stand a chance at defeating it.
A plot could involve Goku and Captain Marvel being on opposite sides of a moral dilemma. For example, Goku might be more focused on a pure battle for the sake of getting stronger, while Captain Marvel is more concerned with protecting the innocent. This conflict could lead to some intense battles between them at first, but then they discover a greater threat that makes them see eye - to - eye. Also, they could be in a story where they are both summoned to a strange new world and have to rely on each other to find a way back home. Maybe they find a powerful artifact there that has the power to change the balance of power in their respective universes.
One idea could be that Naruto and Captain Marvel are brought together by a powerful cosmic force. They have to combine their unique abilities, Naruto's ninja skills and Captain Marvel's superpowers, to defeat a common enemy that threatens both their worlds. For example, a powerful alien race that is draining chakra from Naruto's world and energy from Captain Marvel's universe.
One idea could be Captain Marvel bringing back some alien tech that the Avengers have to figure out how to use. It could lead to new powers for some of the members or a new way to defend Earth.
One idea could be that Goku and Goku Black are forced to team up against an even greater threat from another universe. They start to understand each other's fighting styles during the battle and gradually develop a grudging respect for one another.
Maybe the goddess has a prophecy about Goku being the key to saving her realm from an ancient evil. So she forms a bond with Goku, and as they get to know each other better, Goku starts to develop feelings for her. Their relationship then becomes a driving force for him to fulfill the prophecy and defeat the evil, all while exploring the unique aspects of their two different worlds.
In a fanfiction, there could be a scenario where an ancient prophecy foretells of a combined power of Trunks and Goku being the only thing that can stop an impending doom. They start training together to master a special fusion technique that no one has ever attempted before. Along the way, they face challenges not only in their training but also in dealing with their own egos and differences in fighting styles.
A really interesting plot could be set in an alternate universe where Goku and Launch are arranged to be married for some political reason in the Saiyan or Earthling world. They start off not really liking each other but as they face challenges together, they fall in love. For example, they have to deal with a group that is against their union and in the process, they learn about each other's strengths and weaknesses.
Perhaps in a different universe, Turles and Goku are brothers. They grow up together, training side by side, but then a prophecy divides them as they are told one must defeat the other for the greater good. This creates a complex relationship full of love, rivalry, and moral dilemmas.
A crossover with Doctor Strange could be really cool. Maybe they have to deal with a magical threat that is spreading across different dimensions. Captain Marvel's strength and Doctor Strange's magic would create an interesting dynamic as they try to figure out how to stop it.
A plot could be about an alternate universe where Captain Marvel is initially distrusted by the Avengers. She has to prove herself and in the process, they all learn more about each other's powers and pasts. This could lead to some great character development and new alliances within the team.
What if the powers of Captain America and Captain Marvel get swapped? Captain America suddenly has to deal with the overwhelming cosmic powers while Captain Marvel has to rely on her combat skills and leadership on the ground. This forces them to see the world from each other's perspective and also creates a whole new set of challenges as they continue their mission.