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.
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.
She - Hulk's legal background would add an interesting dimension. The Justice League often deals with complex situations that could involve legal aspects. She could help them navigate through any legal loopholes or treaties. For example, if they have to deal with an international incident caused by a supervillain, she could be the one to sort out the legal implications.
One possible plot could be that the Hulk is somehow transported to the DC universe and is initially seen as a threat by the Justice League. They might try to subdue him, but then realize he's not entirely a villain. Maybe there's a common enemy that forces them to team up. For example, a powerful alien force that is causing destruction in both the Marvel and DC universes. The Hulk's brute strength combined with the Justice League's diverse powers could make for an epic battle against this enemy.
One possible plot could be She - Hulk joining the Justice League on a mission to stop a powerful alien threat. She - Hulk's strength and legal expertise could come in handy. For example, she might use her knowledge of the law to deal with any diplomatic issues that arise during the mission while using her brute strength to fight the aliens.
Hermione is used to working in a team at Hogwarts. So she would likely adapt well to the Justice League's group dynamic. She could form special bonds with different members. For example, she might bond with Wonder Woman over their mutual strength and intelligence. And with Flash, she could share her experiences of using quick thinking in difficult situations. Her presence would add a new layer of complexity and versatility to the League's interactions.
One way it could work is by having a threat that requires both the Hulk's strength and the Justice League's diverse powers. For instance, an alien invasion that has technology to nullify the League's powers partially. The Hulk's physical strength would be unaffected, so he could be the key to victory.
Well, in this fanfic, the Hulk could bring a new dynamic to the Justice League. His lack of restraint might force the League to adapt their strategies. For example, Batman would have to figure out how to control Hulk's rage. And Wonder Woman might find herself in a position where she has to protect Hulk from his own self - destructive tendencies while also using his power to their advantage. It could be a story full of conflict and cooperation.
The combination of Hulk and Superman would be really interesting. You have two extremely powerful beings. Superman's moral compass and the Hulk's uncontrollable rage would create a great dynamic. They could have a friendly sparring match where Superman has to figure out how to hold back the Hulk without hurting him. Or they could team up against a powerful foe, with Superman using his flight and heat vision while the Hulk does his smash attacks.
One great aspect of Justice League Batman x Superman fanfiction is the exploration of their complex relationship. Writers often delve into how their different ideologies can either clash or complement each other. For example, Batman's more grounded and often cynical view versus Superman's idealistic approach.