The Justice League typically includes well-known heroes like Superman, Batman, Wonder Woman, The Flash, Green Lantern, Aquaman, and others. These characters form the core team.
If Sasuke Uchiha met the Justice League, there could be a clash of ideologies at first. Sasuke, with his ninja code and thirst for power, might see the Justice League's more 'righteous' ways as naive. But he could also learn from them about teamwork on a grander scale. Maybe he'd end up joining them in a battle against a common enemy, using his Sharingan to analyze their opponents' moves and lending his ninja skills to the fight.
If Danny Phantom haunts the Justice League, it could be chaos. Danny's ghostly powers would likely surprise the heroes. He might play pranks on them at first, like making Batman's gadgets malfunction or making Superman's cape flap uncontrollably. But it could also turn serious as they might mistake him for a villainous spirit and try to stop him.
The Justice League Marine Girl in fanfiction is often an original character created by fans. She usually has powers related to the ocean, such as the ability to communicate with sea creatures, control water, or swim at super - fast speeds.
I think Flash himself would be really interested. After all, it's about him. He'd be curious to see how the writer of the fanfiction portrays his character, his powers, and his relationships with the other members of the Justice League.
Batman is often a very popular character. In fanfiction, he can be portrayed in different ways, like a more nurturing mentor figure to the Young Justice team or as a master strategist leading the Justice League in complex battles.
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.
Some members might be shocked. Wonder Woman, for instance, who respects Batman's skills and tenacity, would likely be very disappointed. She might try to persuade him to stay, emphasizing the importance of his presence in the team. Superman, on the other hand, might initially be understanding, as he knows Batman has his own way of doing things. But he would also be concerned about the power vacuum that Batman's departure would create. Aquaman might be more indifferent, thinking that Batman was always an outsider to some extent, with his focus mainly on land - based issues.
In a Naruto in Justice League fanfiction scenario, Naruto would have a lot to offer. He has a vast amount of chakra which could be used for various purposes like powering up the League's technology or creating barriers. His relationship with his teammates in Naruto like Sasuke and Sakura could be paralleled with the relationships in the Justice League. Naruto might have some initial cultural clashes with the League members as he comes from a different world, but over time, he would learn to adapt and they would learn from his unique skills and way of thinking. His Sage Mode would give him an edge in battles, allowing him to sense danger more acutely and react faster.