Well, one interesting concept could be the clash of different cultures. When two species meet for the first time in a war scenario, their values, languages, and social structures collide. For example, one species might value honor in combat in a very different way than the other. Another concept could be the technology exchange or the struggle for technological superiority. If one species has a more advanced weaponry, how does the other species adapt? And also, the moral dilemmas that characters face. Do they show mercy to an alien species they don't understand? Or is it all about survival?
One interesting concept could be how different species in the Star Wars universe react to first contact with a new, unknown species. For example, the Jedi might approach it with a sense of curiosity and a desire to maintain peace. Another concept could be the technological exchange that occurs during first contact. Maybe a less - advanced species discovers new ways of using the Force or advanced weaponry from a more - developed one. Also, cultural clashes are likely. A species with a strict hierarchical society might struggle to interact with a more egalitarian one.
A plot could revolve around a diplomatic mission during the First Contact War. Maybe a group tries to broker peace but faces many obstacles from both sides' extremists. This could explore the complex politics and cultural misunderstandings that fuel the war.
In War of the Worlds fanfic, a common concept is the survival of the individual in the chaos. Some stories focus on a single character's journey through the desolate, war - torn landscape. They might have to scavenge for resources, avoid both alien and human threats. Also, the idea of the aliens having a weakness that is not in the original story is often explored. Maybe it's a certain frequency of sound or a type of plant that can harm them. This gives the humans a glimmer of hope in an otherwise hopeless situation.
One interesting concept could be the exploration of different alliances within the Beacon setting during the civil war. For example, how different groups of characters come together based on their beliefs or survival instincts.
The relationships between the characters can also be an interesting concept. In the fanfic, characters who may not have interacted much in the original could form strong alliances or rivalries. It can show how different personalities clash or complement each other in unexpected ways.
One interesting concept could be the exploration of post - war societies. In great mushroom war fanfic, we might see how different groups have rebuilt or are struggling to rebuild. Another concept could be the origin of the war itself, like what led to such a catastrophic event. Also, the evolution of characters in this war - torn setting is fascinating, as they adapt to survive and find meaning in a desolate world.
One idea could be that the aliens come in peace but their appearance is so strange that humans initially panic. For example, they might be made of a substance like jelly and can change their shape at will.
The story of Columbus arriving in the Americas can be considered a form of first contact. For the native people, it was the first time they were encountering Europeans. This contact had a profound impact on both cultures, leading to exchanges of goods, ideas, but also unfortunately, diseases and conflicts. It changed the course of history for both the Old World and the New World.
A great plot could be centered around a diplomatic mission during the war. Maybe a small group of humans and Turians who are trying to find a way to end the war before it gets out of control. They have to overcome their cultural differences and the distrust between their species. There could be a lot of internal conflicts within the group as well as external threats from those who don't want the war to end.
One interesting concept could be the crossover of characters. For example, imagining Shepard from Mass Effect in the Gears of War universe facing off against the Locust horde. It would be fascinating to see how his biotic abilities would interact with the brute force combat of the Gears of War world.