A plot could involve a time - traveling villain who tries to change the outcome of a significant event on an Independence Day in the past, which would have a huge impact on the present. The young justice members must travel back in time to stop the villain and preserve the timeline.
Perhaps the heroes discover a plot by a super - villain to use the patriotic fervor of Independence Day to his advantage. He plans to brainwash the population using a mind - controlling device disguised as a fireworks display. The young justice team has to figure out how to stop this without ruining the holiday spirit for everyone.
One idea could be an OC who is a brilliant scientist that discovers a new weakness in the alien technology just in time for the Independence Day battle. Another could be an OC who is a pilot from a small town and has to step up and fight the aliens, bringing a sense of hometown heroism to the story. Maybe an OC who is a diplomat trying to negotiate with other countries during the alien invasion to unite the Earth's defenses more effectively.
One idea could be to write about an alien invasion on Independence Day but with a twist where the ordinary citizens use their knowledge of American history and values to outwit the aliens. For example, they might use the concept of unity from the nation's founding to band together in a way the aliens don't expect.
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.
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.
One idea could be a misunderstanding that leads to a battle. Maybe a villain manipulates the situation so that Young Justice thinks the Justice League has turned evil. For example, the villain uses mind - control technology on some of the League members and Young Justice has to fight to save them.
One idea could be that the Young Justice team gets accidentally transported to an alternate dimension where the Justice League has turned evil. The Young Justice members then have to figure out how to reverse the situation while also evading capture from their once - heroes. Another could be a time - travel plot where the Young Justice team travels back in time and teams up with the early days of the Justice League to stop a threat that was thought to be long gone but has resurfaced in their own time. A third idea is that a powerful new villain emerges who can only be defeated by a combined effort of the Young Justice and Justice League, but first they have to overcome their differences in fighting styles and leadership.
One idea could be a misunderstanding that leads to a fight. Maybe the Justice League mistakes some of Young Justice's actions as being too reckless and end up in a battle. Then they realize they were wrong when a real threat emerges and they have to work together.
One idea could be a crossover between the two groups. Maybe the Young Justice team discovers a new threat that is related to the Runaways' past. They could team up to fight a common enemy, like a powerful villain who has been manipulating events from the shadows.
A great plot for Young Justice Invasion fanfiction might be to have the team deal with internal conflicts during the invasion. Maybe there are trust issues among some members because of secrets that come to light. For example, if a member was unknowingly related to one of the invaders. This would create drama and force the team to work through their issues while also fighting the external threat. Also, you could explore how the invasion affects the public perception of the young heroes. Are they seen as saviors or are people scared of them bringing more danger?
One idea could be exploring the characters' lives during peacetime. For example, how they adjust to normal life after all the battles. Maybe they start going to school like normal teens and facing typical high school problems while still having their superhero identities in the background.