Well, in such a fanfiction, the story might start with some sort of misunderstanding. Perhaps the Justice League mistakes Danny for a threat. Danny, being a hero in his own right, would not back down. He might first try to reason with them. But if that fails, he'd engage in a battle. His ability to turn invisible could make it really difficult for the League to track him, especially for heroes like Wonder Woman who rely on their eyesight in combat.
A fanfiction of Danny Phantom fighting the Justice League would be a clash of two different power systems. Danny, coming from a world where he battles ghosts, has a different style of combat. The Justice League is used to fighting super - villains on Earth. Danny could potentially use the environment in a ghostly way, like phasing through buildings to set up ambushes. The League would have to adapt quickly to his unorthodox fighting style, and it would make for a very interesting story with lots of potential for character development and epic battles.
I think it could be Superman. Superman is all about truth and justice and he would likely see the good in Danny. Also, they both have super strength in a way. Danny has his ghostly strength and Superman has his Kryptonian strength. They could bond over protecting the innocent.
I'm not entirely sure as I haven't read this specific fanfiction. It could be about a disrupted or alternative version of a story where Danny Phantom interacts with the Justice League in some unexpected or 'broken' way.
In a 'danny phantom vs justice league' fanfiction, Danny could use his ghost powers to surprise the Justice League members. His intangibility and invisibility might give him an edge at first. Maybe he'd startle Superman by suddenly phasing through a wall. However, the Justice League has a vast array of powers and skills too. Batman could potentially figure out Danny's weaknesses with his detective skills. And Wonder Woman with her combat experience could pose a real threat to Danny in a face - to - face battle.
One common theme is the clash of two different worlds. Danny comes from a world where ghosts are a big part of his life, and the Justice League is from a more traditional superhero world. So there's often a theme of how they deal with each other's differences.
I think Superman would be the most likely. Superman is known for his kind heart and open - mindedness. He would probably see Danny as a young hero in need of some guidance and friendship. He wouldn't be too quick to judge Danny based on his ghostly appearance or powers.
His powers would be quite complementary. His flight ability could match up with Superman's in some ways. And his ecto - energy based attacks could add a different type of offensive power to the team.
Danny could use his ghostly powers to disrupt the technology that some Justice League members rely on. For example, he could mess with Cyborg's systems. His ability to overshadow people might also be a key factor, allowing him to control some of the less - powerful members.
Another storyline might involve Danny being wrongly accused by the Justice League of a crime he didn't commit. As he tries to prove his innocence, he uncovers a deeper conspiracy that threatens both the human world and the Ghost Zone. He has to use his wits and powers to clear his name and save the day.
In this fanfiction, perhaps Danny Phantom discovers a plot against the Justice League early on. He then uses his invisibility and intangibility to gather information. His ability to fly and super strength (in his ghost form) would be crucial in battles against the villains targeting the League. For example, if the villains had some sort of kryptonite - like weapon against Superman, Danny could use his powers to either disable the weapon or protect Superman until they find a way to neutralize it.
One possible plot could be that Danny Phantom is facing a threat in his own dimension that is beyond his control. He decides to call the Justice League for help. Maybe he first has to figure out a way to contact them across dimensions. Once he does, the Justice League initially doubts his claims but as they start to investigate, they realize the severity of the situation and they all work together to fight the new and strange enemies from Danny's world.