A storyline could involve Goku Black being sent to the DC Universe by Zamasu as part of a plan to conquer new worlds. The Justice League initially tries to reason with him, but he attacks. Superman and Goku Black have an epic battle in the skies, with their powers causing massive destruction. Meanwhile, Batman is researching a way to stop Goku Black's ki attacks. Wonder Woman joins the fight, using her lasso to try and restrain him. As the battle progresses, the Flash realizes that Goku Black's power has a pattern and he tries to disrupt it. In the end, they either defeat Goku Black or find a way to send him back to his own universe. There could also be a story where Goku Black teams up with Lex Luthor who promises to help him defeat the Saiyans in exchange for Goku Black helping him take over the world.
In a fanfiction, the story could start with Goku Black sensing the powerful energy of the Green Lantern Corps. He travels to their sector to test his strength against them. The Justice League is called in to assist. Goku Black quickly shows his dominance in combat, but the League's unity starts to give him trouble. Aquaman uses his control over the sea to try and slow Goku Black down. Cyborg analyzes Goku Black's power and tries to find a technological way to counter it. As the story unfolds, the heroes start to learn more about Goku Black's motives. It could end with a final showdown where the Justice League uses a combined attack of all their powers to either defeat Goku Black or, in a more interesting twist, convince him to change his ways and use his power for good in the DC Universe.
One possible storyline could be that Goku Black arrives on Earth in search of a powerful energy source. The Justice League detects his arrival and confronts him. At first, they underestimate his power. Goku Black easily defeats some of the members, but then the League starts to work together and figure out his weaknesses. Another storyline could be that an evil entity has brought Goku Black to the DC Universe to cause chaos and the Justice League has to stop him while also dealing with the entity. Or perhaps Goku Black is tricked into thinking the Justice League are enemies of the Saiyans and he attacks them, only to later find out the truth and have to team up with them to fight a greater threat.
One possible storyline could be that Naruto is somehow transported to Goku Black's universe. There, he has to face Goku Black who sees him as an intruder. Naruto would have to quickly learn about Goku Black's powers and find a way to fight back using his ninja skills. Another storyline could be that a powerful villain creates a rift between their two universes and pits them against each other. They start off as enemies but then realize they are being manipulated and team up to fight the real villain.
There could be a storyline where Beerus, out of boredom, decides to train Goku Black instead of fighting him. But Goku Black misinterprets this as a sign of weakness and attacks Beerus. This could lead to a battle where Beerus has to hold back at first to avoid killing Goku Black, but as the fight progresses, he realizes he has to use his full power to subdue him.
One possible storyline could be that Batman discovers a conspiracy within the Justice League that endangers Gotham. So he and Robin decide to take on the League to stop it. Another could be that the Justice League is being mind - controlled, and Batman and Robin are the only ones who realize it and try to free their friends by fighting them. Or perhaps there's a misunderstanding where the Justice League believes Batman and Robin have turned bad, and they have to fight to prove their innocence.
In a Goku Black - Justice League fanfiction, it's possible that Goku Black would initially be seen as a threat. But if there was some sort of deal or situation that made him side with the League, he could add a whole new level of power. His fighting style, which is very different from the traditional Justice League members, could make for some exciting battle scenes. He might even teach the League some new combat techniques.
A third possible storyline could be a story of misunderstanding at first. The two groups could initially see each other as threats. For instance, the Justice League might mistake the Z - fighters' high power levels as a sign of aggression. However, through a series of events and battles, they come to realize that they are on the same side and must work together to face greater threats. This could involve some epic one - on - one battles between characters like Vegeta and Superman before they finally team up.
Another storyline might involve Batman leaving because of a personal crisis. For example, he discovers something dark about his past that makes him question his place in the Justice League. He might think that he's a liability to the team and decide to leave to protect them.
In fanfiction, Goku Black could be incorporated into the Justice League as a sort of experiment. The League, always looking for ways to increase their power and protect the world, might see his abilities as a valuable asset. However, his different moral code and origin from another universe would create a lot of tension. There could be a story arc where the League tries to reform him or at least control his more violent tendencies while using his power to fight against threats that are beyond their normal capabilities.
One possible storyline could be that Goku is accidentally transported to Alucard's world. They start off as enemies but then gradually learn about each other's powers and come to respect one another. Another could be that a powerful villain manipulates them into fighting each other. In this case, they might realize they are being used and team up against the real enemy.
One scenario could be Naruto using his clones to distract the Justice League while he sneaks up on Superman and uses a powerful jutsu. Another could be the Justice League trying to find Naruto's weakness, like his connection to the nine - tailed fox, and Naruto having to defend himself against their attacks. Maybe Batman tries to analyze Naruto's fighting style and come up with a plan to defeat him.
One possible storyline could be a joint mission against a powerful new villain. The Batfamily's detective skills combined with the Justice League's raw power would be a great combination. Another could be a sort of 'cultural exchange' where the League members try to understand the Batfamily's no - kill rule and the family tries to adapt to the League's more open - ended approach to heroism.