Maybe in the fanfiction, the Hulk's gamma radiation has an unexpected effect on some of the Justice League members. For example, it could give Superman a new vulnerability or temporarily enhance the powers of Flash in a strange way. This leads to a complex situation where they need to both deal with the Hulk and the consequences of this new development.
One idea could be X23 joining the Justice League on a mission to stop a powerful mutant - hating villain. Her unique combat skills and mutant abilities would add an interesting dynamic to the team.
One idea could be that a powerful cosmic entity threatens both universes. The Justice League and the Avengers initially clash due to misunderstandings in their attempts to deal with it. But then they realize they need to work together. They combine their powers and strategies, like Superman's strength with Hulk's brute force and Batman's intellect with Iron Man's technology. This could lead to epic battles and heroic sacrifices as they strive to save both universes.
One idea could be that the OC has a unique power that the Justice League initially distrusts but later comes to rely on. For example, the OC can manipulate time in small bursts, which at first seems dangerous but is actually crucial in stopping a villain who can freeze time.
One idea could be a crossover where the Young Justice team has to team up with the Justice League to face an interdimensional threat. Maybe a powerful villain from another dimension is trying to invade Earth and the combined skills and powers of both groups are needed to stop it.
Maybe a story where some of the younger members of the Young Justice team are frustrated with the Justice League's methods and decide to take on a mission on their own, but end up getting in over their heads and have to call in the League for help. This could lead to a lot of character development and some interesting dynamics between the two groups.
A plot could revolve around a scientific experiment gone wrong that affects only them. They start to lose control of their powers in different ways. Hulk might become too calm and lose his rage - fueled strength, while She - Hulk might turn into her human form at the wrong times. They have to work together to reverse the effects of the experiment, all while dealing with the problems that come with their power - changing states.
One idea could be that they team up to face a new super - villain who is immune to normal Hulk - like strength. So, they have to combine their smarts and unique Hulk - related abilities in a new way. Another could be a story where they explore their family connection in a more in - depth way, like dealing with the implications of being related Hulks in a world that still doesn't fully understand them.
Perhaps Trunks is initially mistaken for a threat by the Justice League. But as they learn more about him and his mission to protect his own timeline, they start to work together. For example, Trunks could share his knowledge of advanced Saiyan fighting techniques with Batman, who then uses this knowledge to develop new strategies for the team. Meanwhile, Wonder Woman could teach Trunks about the different cultures and values in the Justice League's world.
One idea could be a tournament where the Z - fighters from Dbz and the Justice League members compete. For example, Goku could be paired against Superman in a friendly yet intense battle to see who is stronger in terms of physical strength and combat skills. Another plot could involve a common enemy that forces the two groups to team up. Maybe Darkseid and Frieza form an alliance and the combined forces of the Dbz characters and the Justice League have to stop them.
Definitely Superman. He has the strength and the moral compass to try and understand the Hulk. He can also withstand the Hulk's attacks to a certain extent, so he could be the first to approach the Hulk and attempt to form an alliance. He might see the good in the Hulk, similar to how he sees the potential for good in Lex Luthor at times.