Friendship is a key element. Their relationship starts as a friendship based on mutual trust. For example, in many fanfics, Bumblebee is always there to protect Sam, and Sam in turn tries to understand Bumblebee's needs and feelings.
Archive of Our Own (AO3) is also a great place. There are many well - written and diverse bumblebee x sam fanfics there. You can use the search function to easily find what you're looking for.
One great bumblebee x sam fanfic could be 'The Bond Beyond Metal and Flesh'. It explores their unique friendship in a more in - depth way, showing how they rely on each other in various situations.
There's also 'Sam and Bumblebee: A New Adventure'. In this fanfic, they go on a journey through an unknown dimension. The author does a wonderful job of exploring their relationship in a unique setting, and it has some heartwarming moments as they rely on each other to survive.
Another aspect could be that Sam starts to develop a new friendship with a human who is also interested in the Transformers. Bumblebee doesn't like this new person at all because he's afraid of losing Sam's attention. So, Bumblebee starts to act in a more possessive way, like following Sam around more closely when the new friend is around. Sam has to find a way to balance his new friendship and his relationship with Bumblebee.
Well, in a Transformers fanfiction with Sam and Bumblebee being possessive, it could be about Bumblebee being overly protective of Sam. Maybe in a battle situation, Bumblebee refuses to let any other Autobot or Decepticon near Sam because he sees Sam as his special human friend. He might even go to extreme lengths to keep Sam safe, like taking on multiple enemies by himself just to ensure Sam's well - being.
Well, there are fanfictions where Bumblebee and Sam form a deeper emotional bond. For example, a story where Sam is in trouble and Bumblebee has to go to great lengths to save him. It could show how their friendship has evolved over time. There might also be a fanfiction that focuses on their early days of meeting and how they learned to trust each other.
Another theme could be the discovery of each other's hidden sides. Blitzwing has his multiple personalities, and Bumblebee has his own courage and determination. In fanfics, they often discover new aspects of each other that they didn't expect, which deepens their connection in the story.
In bumblebee x grimlock fanfic, a common theme is acceptance. Bumblebee is small and nimble compared to the large and powerful Grimlock. But they learn to accept each other's differences. There is also the theme of adventure. They embark on various adventures together, whether it's exploring new territories or facing new threats. This allows for a lot of exciting plot developments and showcases their relationship in different situations.