Well, perhaps the cousins start off with some petty rivalry in their present time. Then, through some strange time - travel event, like finding an old family heirloom that's a time - traveling device, they get sent to different eras. In the past, they might compete for the attention of a historical figure, which escalates their catfighting. As they travel through time, they gradually realize that they need to work together to get back to their own time, and in the process, they mend their relationship.
The two cousins are obviously the main characters. They could be very different in personality. One might be more adventurous and impulsive while the other is more cautious and studious. There could also be some side characters like an old time - traveler who accidentally sent them on their time - traveling journey, or a love interest in one of the time periods that causes more tension between the cousins.
Maybe the time travel airplane is a top - secret government project. It malfunctions during a test flight and travels back in time to the age of the dinosaurs. The crew has to deal with all kinds of prehistoric challenges while trying to repair the time - travel mechanism to return to the present day. It's a race against time and nature.
A baby could be wearing a magical diaper that activates time travel. The baby might find itself in ancient Egypt, where the diaper is mistaken for a strange new cloth. The baby's innocent actions could change some small things in that time period. Then the diaper brings the baby back to the present, but the baby has memories of that amazing adventure.
Well, family gatherings could be an important element. Maybe it's a big family dinner where they keep stealing glances at each other and start to feel those new emotions. Another element could be shared secrets. For example, they might have a secret place in the backyard or an attic where they first realize their feelings. Also, reactions from other family members might play a role, like when the family starts to suspect something and they have to deal with that while exploring their relationship for the first time.
The plot could involve Anne Boleyn traveling to a time when women had more rights. She could be shocked at first but then realize the potential for change in her own time. For example, she could learn about feminism and use this knowledge to fight for her position more effectively in her original time period.
Maybe an AI time - travels to a future where all of humanity has vanished. The AI explores the empty cities, trying to figure out what happened. It discovers clues that lead it to understand that a series of bad environmental decisions in the past led to this outcome. The AI then decides to go back and try to change things in the past to prevent this future from happening.
A possible plot could be a woman who travels back to the Victorian era. Due to some time - space anomaly, she starts to experience breast expansion. This causes a stir in the prudish society of that time. She has to figure out how to hide her transformation while also trying to find a way back to her own time. Along the way, she meets a kind inventor who helps her understand the scientific basis of what's happening and they work together to reverse it.
In a time travel plane story, the plane could be an ancient, magical plane that has the power to travel through time. The main character, a young adventurer, stumbles upon this plane and decides to take it for a ride. He travels back to the time of the dinosaurs and has to survive in that prehistoric world. Along the way, he discovers secrets about the origin of the plane and how it can be used to change the course of history.
A plot could be that a time - traveler goes back to WW2 to find a lost relative. They end up getting involved in a dangerous mission. Maybe they help smuggle a group of Jews to safety. Along the way, they fall in love with someone from that era, which complicates their situation as they know they don't belong there.
In the fanfiction, they could both have different dreams. Tony might want to be an artist while Sharon wants to be a scientist. Despite their different paths, they encourage each other. They also deal with family expectations as cousins and find ways to support each other's dreams without sacrificing their family relationship.