One common theme is power and control. Megatron is a powerful figure, and having a human as a 'pet' allows exploration of how he exerts his power over a much weaker being. Another theme is the unexpected bond that can form between two very different entities. Despite their differences, the human and Megatron might develop a relationship that defies expectations.
Well, I know a fanfiction titled 'Megatron and the Human's Adventure'. In this story, the human that Megatron has as a pet gets involved in Megatron's grand plans in a rather unique way. It shows how the human's presence starts to influence Megatron's decisions over time. There is also 'A Human in Megatron's World' which focuses on the human's perspective of being Megatron's pet and how they adapt to the strange world of the Transformers.
One common theme is power dynamics. Megatron is a powerful being, and when paired with a human, the contrast in power is striking. Another theme is the idea of understanding across species. Since they are so different, the fanfictions often explore how they can begin to understand each other.
A common theme is the idea of companionship. Just like in regular human - pet relationships, the human and the Transformer - pet in these fanfictions often rely on each other for emotional support. For example, a lonely person might find a Transformer that fills the void in their life.
Another good one is 'A Human's Encounter with Megatron'. It starts with a chance encounter between a young human and Megatron. As the story progresses, the relationship between them becomes more and more complicated, with themes of trust, power, and survival intertwined.
In a world where the Transformers and Megatron's universe collide, Optimus Prime finds himself in an unfamiliar realm. He discovers Megatron has formed an unlikely alliance with a group of humans. Optimus is initially skeptical but realizes they must work together to face a new common enemy, a powerful energy - sucking creature from another dimension. The story unfolds as they learn to trust each other and combine their strengths.
One popular Transformers human - pet fanfiction might be those that explore the relationship between a human character and a pet - like mini - Transformer. For example, a story where a young girl befriends a small, cute Autobot that has the form of a kitten. In these fanfictions, the interactions often involve the human protecting the Transformer from the Decepticons and the Transformer using its unique abilities to help the human in return.
One possible fanfiction could be about Optimus Prime and Megatron having to team up against a greater threat. Maybe an ancient evil from Cybertron's past resurfaces that is so powerful that their usual enmity has to be put aside. They start off distrusting each other but as they face battles together, they gradually come to respect the other's fighting skills.
A fanfiction could focus on a time when Megatron and Soundwave are separated. Maybe Megatron has been captured by the Autobots, and Soundwave is left to lead the Decepticons in his absence. Soundwave, who is not used to being in the spotlight, has to make difficult decisions. He has to figure out how to rescue Megatron without sacrificing too many of their troops. Meanwhile, Megatron is facing his own challenges in captivity, perhaps having to deal with Optimus Prime's attempts to make him see the error of his ways. This situation could create a lot of tension and drama in the fanfiction.
I'm not sure specifically what'megatron's pet fanfiction' is about without more context. It could be a fan - created story about Megatron having a pet in the context of the Transformers universe, perhaps exploring how a powerful character like Megatron would interact with a pet, whether it's a strange alien creature or something more common - like in a very different take on the character.