A young WW1 infantryman would make a great main character. He could represent the 'old - school' values and combat style of WW1. When he travels to WW2, he has to adapt to the new warfare, and his journey of adaptation could be very interesting to follow.
Well, they could change the course of the war. For example, Iron Man could use his advanced tech to quickly take out enemy tanks. Captain America would feel right at home in a way, fighting alongside soldiers again. And Thor could use his lightning powers to disrupt enemy lines.
One idea could be a soldier from WW1 suddenly finding himself in the middle of a WW2 battle. He might use his old - fashioned combat skills in a new and more advanced war setting. For example, his experience with bayonet charges could be a shock to the modern - day soldiers he meets in WW2.
One idea could be a modern-day historian who accidentally travels back to the Versailles negotiations after WW1. They could try to change the terms of the treaty, knowing the long - term consequences it had. For example, they might attempt to make the reparations more lenient on Germany, which could potentially prevent World War II.
A common character is the time traveler themselves, usually someone from the modern day. There are often soldiers, both Allied and Axis, like a brave American GI or a determined German officer. Civilians also feature prominently, such as a French Resistance fighter or a British housewife trying to survive the Blitz. And sometimes, there are historical figures like Winston Churchill or Adolf Hitler who the time traveler may interact with.
Soldiers are very common. They could be from either side, like an Allied soldier who goes back in time to give strategic advice, or a German soldier who has a change of heart and tries to alter the course of the war. Another common character is the civilian time traveler. They might be a historian who wants to experience the war first - hand or a regular person who accidentally gets sent back in time.
One great 'Avengers Time Travel Fanfiction' is 'Time's Heist Redux'. It takes the concept of the time heist from the movies and expands on it in really interesting ways, like exploring different timelines the Avengers could have messed up in.
One interesting WW2 time travel fanfiction could be about a modern-day historian who travels back to WW2. They might use their knowledge of the war to change small events and see how it affects the overall outcome. For example, they could prevent a key intelligence leak that would have otherwise given the enemy an advantage.
Some common themes in WW1 time travel fanfiction include the alteration of historical events. This could be something like a time traveler trying to save a loved one who died in the war. There's also the theme of cultural clash. A modern - day person suddenly in the WW1 era would face differences in fashion, language, and values. And a prevalent theme is the butterfly effect. A small change made by the time traveler can have huge and unexpected consequences on the course of the war and history in general.
One interesting plot could be a modern person traveling back to WW2 and using their knowledge of future technology to help the Allies in a covert way, like improving communication systems. Another could be a time traveler trying to prevent a particular tragic event during the war, such as the bombing of a certain city. And there might be a plot where the time traveler has to adapt to the harsh wartime conditions and forms unexpected friendships with soldiers on the front line.