Captain America is also a key focus. His leadership qualities are highlighted. He could be seen rallying the other Avengers as they watch the trailer, giving inspiring speeches about not giving up and fighting for the universe.
Well, in some of the fanfictions, there are characters showing shock and disbelief. For example, some characters might be seen crying as they watch the trailer, realizing the enormity of what's to come in Endgame. It really adds an emotional depth to the pre - Endgame scenario.
By focusing on the key moments from the trailer. For instance, if the trailer showed a powerful new weapon, the fanfiction might have characters speculating about its power and how it will be used in the movie. It could also show characters' reactions to the new looks of the heroes, like Thor's new physique, which was quite different in Endgame.
There could also be some analytical reactions. Fans in the fanfiction might be dissecting every frame of the trailer, trying to figure out how the story will unfold. They could be speculating about new suits, new alliances, and what the final battle will look like. They might be discussing whether certain characters will die or not based on the trailer's hints.
It could strengthen them. For example, Black Widow and Hawkeye might have a closer bond as they both see the enormity of the situation in the trailer. They might rely on each other more, knowing that they need to be there for one another in the upcoming battle.
One popular type of fanfic might be where the Avengers are in the compound and they all gather to watch the Endgame trailer. They could have various reactions. For example, Tony Stark might make some sarcastic comments about how they made the trailer look so epic. Steve Rogers could be more solemn, thinking about the implications of what's shown in the trailer for their upcoming battle. And Thor might be a bit confused at first, but then get fired up as he realizes the importance of what they're about to do.
Archive of Our Own (AO3) is also a great place. It has a very active community of fanfic writers. Many of them write unique takes on the Avengers watching trailers. You can use the tags to narrow down your search, like 'Avengers' and 'trailer' tags.
I really liked 'The Avengers: Trailer Reaction by a New Recruit'. It was exciting as it showed a new character's perspective while watching the trailers for the first time. The author did a great job of capturing the anticipation and awe that comes with seeing the Avengers in action.
Captain America could have a more determined look. In fanfiction, he would likely see the trailer as a call to action, a chance to rally the team even more. He'd probably think about how to boost the morale of the Avengers and the rest of the world. His reaction would be about inspiring hope in the face of such a seemingly hopeless preview.
Some 'Avengers Watch Endgame' fanfictions focus on the reactions of the Avengers during the viewing. For example, Thor might have a more emotional breakdown seeing his past self struggle so much, or Tony Stark could be making sarcastic comments throughout the viewing, which both add humor and depth to the story.