One idea could be a battle where the Eternals and Avengers are initially at odds due to a misunderstanding. Maybe they both think the other group is causing some strange cosmic events. Eventually, they figure out it's a third party and team up.
A plot could involve an Eternal having a special power that the Avengers need to defeat a new, extremely powerful villain. The Eternal joins the Avengers on a mission, and during the process, they learn about each other's cultures and fighting styles. For example, the Eternals' long - lived perspective clashes with the Avengers' more immediate, Earth - based concerns. This leads to some interesting character development and team - building moments.
One idea could be exploring the backstories of the Eternals in more depth. For example, how they first arrived on Earth and their initial reactions to this new planet. Another could be a love story between two Eternals that was previously untold, perhaps a forbidden love due to some ancient Eternal law. A third idea is to create a story where the Eternals have to team up with modern superheroes to face a new, greater threat that neither could handle alone.
One idea could be that Spiderman discovers a new threat in his neighborhood which turns out to be linked to a much larger plot involving the Avengers. So he has to convince the Avengers to take him seriously and work together to stop it.
One idea could be Deadpool trying to join the Avengers but constantly annoying them with his non - stop chatter and crazy antics. For example, he could keep interrupting their strategy meetings with his own hare - brained plans.
In fanfiction, if the Avengers meet the Eternals, there could be an epic battle at first due to misunderstandings. The Avengers might see the Eternals' powerful abilities as a threat. But then they could realize they have a common enemy and team up. For example, they might face a new, powerful cosmic villain together.
One plot idea could be that the Avengers find Stan Lee's old unpublished comic scripts during an adventure. They then use the ideas in the scripts to defeat a new, powerful villain who is immune to their usual tactics. Another could be that Stan Lee, as a spirit, visits the Avengers to give them moral support and some secret wisdom before a big battle.
One idea could be that the Avengers need the Agents of Shield's help to track down a new, powerful and elusive villain who has technology that can disrupt the Avengers' powers. The Agents use their espionage skills to gather intel while the Avengers provide the muscle when it comes to confronting the bad guy.
A possible plot could be that the meeting causes some sort of time rift. The Avengers then have to fix this rift while also dealing with the differences between their present and past selves. Their past selves might be more naive or idealistic in some ways, which could lead to both comical and tense situations.
A cool Eternals fanfiction could center around the powers of the Eternals. Imagine a story where Druig uses his mind - control powers in a more complex and morally ambiguous way. Maybe he tries to control a powerful human leader to bring about world peace but faces opposition from the other Eternals. Also, a fanfiction about the Eternals adapting to modern - day Earth after being away for so long would be interesting. They would have to deal with new technologies and cultural changes.
You could write a fanfiction where some of the Eternals get separated from the group and have to survive on their own in a hostile part of the world. They would have to use their powers in new and creative ways to stay alive and find their way back to the others. This would show their individual strengths and weaknesses more clearly.
One great 'Avengers watch Eternals' fanfiction could be one where the Avengers are in shock at the powers and history of the Eternals. They might be watching some sort of recording about the Eternals' past battles. Another could involve them watching the Eternals interact on their home planet and the Avengers learning about their complex social structures.