Sam's baby sister could also be depicted as a mediator. In a story where there are conflicts between different groups of Transformers on Earth, her naivete and lack of prejudice could help bridge the gap. She doesn't understand the reasons for their fighting and just wants everyone to get along, which could gradually influence the Transformers to find common ground.
One possible fanfiction could be about Sam's baby sister being born with a special connection to the Transformers. Maybe she can communicate with them telepathically. This could lead to all sorts of adventures where she helps the Autobots in ways that Sam couldn't. For example, she might be able to sense when the Decepticons are planning a surprise attack and warn the Autobots in time.
One popular type of 'Family Matters' fanfiction involving Baby Sister Sam could be a story where she discovers a hidden talent. For example, she might find out she has an amazing singing voice and then has to deal with the newfound attention it brings in the family and at school.
He can be depicted as a bit of an eccentric in fanfiction. His intense focus on his scientific work might lead to some humorous situations. Maybe he gets so caught up in his experiments that he forgets about the time or causes some minor chaos in the human - Transformer shared environment.
Obviously, Dean and Sam are main characters. They are the protective older brothers. And then there's the baby sister, who is likely a central figure as well, with her own personality and role in the fanfiction. There might also be other recurring characters from the 'Supernatural' universe like Castiel who could play important parts in the story.
In Supernatural fanfiction, Sam having cancer can be portrayed in various ways. Some authors might use it as a way to add more emotional depth to his character. They could show his struggle with the illness while still dealing with the supernatural threats. For example, he might be weaker physically but still determined to fight demons, which creates a contrast between his human vulnerability and his heroic side.
Another way is to follow Supernatural fanfiction writers on social media platforms. They often share their works or recommend other good stories. For example, on Twitter, there are many Supernatural fanfic writers who are active and can give you great suggestions for Sam and Dean baby sister fanfictions.
One interesting storyline could be the baby sister having special powers that she has to learn to control. Maybe she can communicate with spirits in a unique way, different from Sam and Dean, which adds a new dynamic to their hunting adventures.
In Avengers fanfiction, Thor's sister can be depicted in many ways. One common way is as a mysterious figure. She might have secrets about Asgard that even Thor doesn't know. Writers also tend to give her unique relationships with other Avengers members. For instance, she could have a special bond with Loki, which adds an interesting dynamic to the story.
Their relationship could be portrayed as a partnership in parenting. Sam and Danny work together to teach their kids the values they believe in, whether it's about respecting all living beings (because of Danny's connection to the ghost world) or being true to oneself (which is something Sam has always been about). They also share the responsibilities of taking care of the household and making sure the kids are happy and healthy.
There could be a really interesting fanfiction where Female Sam is a mechanic who catches Optimus' attention. Maybe she helps repair him in a unique way and they form a bond based on mutual respect for each other's skills.