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.
Baby Optimus Prime's character can be developed by exploring his relationships. If he has a mentor figure among the Autobots, his interactions with that character can shape him. He might look up to this mentor and try to imitate their good qualities. His relationship with other baby Transformers or younglings can also be important. He could learn about sharing, cooperation, and friendship through these relationships. Additionally, his discovery of his own strength, both physical and mental, can be a key part of his development. For instance, when he first realizes he can lift a small object that others thought was too heavy for him, it gives him confidence.
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.
Perhaps there's a fanfiction where the humans are using bath bombs in a large bath tub they've set up near the Autobot base. Optimus and Ratchet come across this strange activity. The humans explain that it's a way to unwind. Optimus, being the diplomatic leader, decides to learn more about this human custom. He asks the humans various questions about bath bombs, like what they are made of and why they fizz. Ratchet is more concerned about the practicality but eventually gets drawn into the fun as the humans start sharing stories about how much they love bath bombs.
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.
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.
There could be a fanfiction where baby Optimus Prime is sent to the past, to a time when the Transformers' society was very different. He has to adapt to the old ways while still holding onto his future - self's values. He might meet young versions of his future friends and enemies, and his presence starts to change the course of history in small but significant ways.
There's also a fanfic called 'Healing Hearts'. In this story, Ratchet plays a crucial role in mending Optimus after a particularly difficult battle. The author does a great job of exploring their friendship that could potentially be more. It has some really touching moments that make it a great read for fans of the pairing.
Secondly, create a unique setting. Instead of the usual battle - torn Cybertron, set the story in a parallel universe where the Autobots and Decepticons have different roles or in a post - apocalyptic Cybertron where they have to rebuild together. This can add a fresh perspective to their relationship.
They could be incorporated by having the humans use bath bombs as a form of celebration. For example, when the Autobots achieve a major victory, the humans decide to have a party and use bath bombs as part of the celebration. Optimus and Ratchet are invited to join. Optimus might see it as a way to bond with the humans further, while Ratchet would be more interested in the scientific aspect of how the bath bombs work.