Well, a very frequent theme is the struggle between their duties and their feelings for each other. They are warriors first, so they have to balance their personal emotions with their responsibilities towards their team. Also, the theme of growth in their relationship is common. They start from a certain point and as the story progresses, their bond deepens in different ways.
Another theme is the idea of a deeper connection. It could be a romantic or a very deep platonic connection. Many fanfics explore how they understand each other on a level that others in the Autobot team may not. They share glances, have private conversations that show the special nature of their relationship.
There's a fanfic called 'Arcee's Trust'. In this, the relationship between Optimus and Arcee is explored in a very unique way. It shows how their bond grows over time. The author does a great job of writing their dialogues, which seem very in - character. It's a great read if you like stories that focus on character development.
Love and loyalty is also a big theme. Since it's a relationship - based fanfic, it often explores how they feel about each other. Maybe Arcee has to prove her loyalty to Optimus in a difficult situation, or Optimus shows his love for Arcee in a selfless way.
One possible storyline could be them facing a powerful new Decepticon threat together. Optimus and Arcee would have to combine their skills, with Optimus using his strategic mind and Arcee her speed and agility. Another could be a story set in a post - war scenario where they are trying to rebuild Cybertron and their relationship deepens during the process. And perhaps a time - travel plot where they go back in time and have to change an event that will save Cybertron in the future.
There are also fanfictions that focus on adventure and teamwork. The two characters might be forced to work together on a mission, and during that time, their relationship blossoms. It could involve things like escaping from a dangerous situation or finding a powerful artifact. This theme allows for a lot of action - packed scenes along with the development of their relationship.
Their relationship can be portrayed as a deep friendship with mutual respect. Optimus, as the leader, respects Arcee's skills and determination. Arcee, in turn, looks up to Optimus and trusts his leadership completely. They can also have a mentor - mentee relationship where Optimus guides Arcee in some aspects.
Romance is also a theme, though it can be a bit tricky in the context of Transformers. Writers often explore the emotional connection between Arcee and Optimus Prime, how they might have a deeper understanding of each other that goes beyond just comradeship.
I really liked 'Silent Conversations'. In this fanfic, the author does an amazing job of showing Soundwave's loyalty to Megatron while also being drawn to Optimus in a way that's both unexpected and fascinating. It's a slow - burn story that builds up the relationship between them gradually, with great character development.
One common theme is the struggle of their relationship within the context of the war. They are both important in the Transformers universe, and the fanfictions often explore how their love survives or is affected by the battles and the overall war situation.
Good character portrayal is key. Since Soundwave is usually a silent and mysterious character, and Optimus is the noble leader, a good fanfic should stay true to these traits while also showing new sides as their relationship develops. For example, Soundwave might show vulnerability only around Optimus.