In such a fanfiction, one possible outcome could be a character using knowledge from WW2 to change the course of WW1. For example, they might introduce more advanced military tactics. Maybe they could try to prevent certain events that led to the large - scale destruction in WW1. However, this would also likely cause a lot of chaos as the timeline is disrupted.
A character's perspective would likely change a great deal. In WW2, they might have seen the full horror of total war, with aerial bombings and large - scale genocide. Going back to WW1, they would find a war that was more 'traditional' in some ways, with battles mainly on the ground. They might be shocked at the naivete of the soldiers in WW1 who were not fully aware of the new forms of warfare that would come in the future.
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.
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.
Here's another story. A group of paratroopers were sent back during a mission. Their plane had mechanical problems. Once sent back, they were redeployed to a different theater of war. They had to quickly adapt to new strategies and fight alongside different units, which was a huge challenge but also an opportunity to learn new combat techniques.
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 possible short story could be about a modern - day historian who accidentally travels back to WW2. He finds himself on a battlefield, witnessing the chaos and heroism. He tries to use his knowledge of the war's outcome to save lives, but quickly realizes that any small change he makes could have huge consequences. For example, he might prevent a key soldier from dying, which then changes the course of a battle and potentially the entire war.
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.