A plot could be that Optimus Prime, in his travels, discovers a lost civilization. There, he meets a female leader who is intelligent and kind. She is intrigued by his noble nature, and he by her leadership and the unique culture of her people. As he helps her protect her civilization from various threats, their relationship blossoms into love.
Perhaps a plot where Bumblebee discovers a hidden power within himself with the help of Optimus Prime in a world filled with lemon - like energy sources. This power could be crucial in saving their planet or defeating a powerful enemy. The story could explore how they work together to harness this power and the sacrifices they might have to make along the way.
A plot could be that the OC is from an enemy faction at first but then realizes the truth about Optimus Prime and his cause. The 'lemon' element might be that they start to fall for each other during a time when they are hiding from their respective sides. Their relationship could be full of secrecy and longing as they try to figure out how to be together in the midst of all the chaos.
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.
One interesting Optimus Prime love fanfiction could be about his relationship with a human female who helps him understand human emotions better. In such a story, they might go through various challenges together while fighting the Decepticons and in the process, their bond deepens.
One possible plot could be that Optimus Prime discovers he's pregnant through some sort of strange energy transfer. He then has to deal with the reactions of his fellow Autobots. Some might be shocked, while others try to support him. Another idea is that the pregnancy is a result of an experiment by the Decepticons gone wrong, and Optimus has to protect himself and the unborn life from their attempts to use it for evil.
A strong female Autobot would be a great love interest. They already share the same values and goals, and the bond of being on the same side in the fight against the Decepticons could easily turn into a deeper emotional connection.
One interesting Optimus Prime fanfiction could be about his origin story in a different universe. Maybe in this story, he was created by a group of ancient beings with a unique purpose.
One common theme could be the struggle between his duties as a leader and his new - found love. For example, he might have to choose between protecting his team and being with the one he loves. Another theme could be the acceptance of his love by his comrades. Since he is in a position of great responsibility, they might be initially skeptical. Also, the idea of an inter - species love could be explored, considering Optimus Prime is a Cybertronian.
Perhaps a fanfiction where Grimlock is initially distrustful of Optimus Prime's more diplomatic approach. But as the story progresses, they learn from each other. For example, Grimlock could teach Optimus about the value of brute force in certain situations, while Optimus could show Grimlock the importance of negotiation. This would lead to a stronger bond between them and a more united Autobot force.
One idea could be an Optimus Prime crossover with the Transformers: Beast Wars. Imagine Optimus Prime interacting with the Maximals and Predacons, and how his leadership style might contrast or blend with that of Primal. Another could be a crossover with a superhero universe like the Avengers. Optimus Prime could team up with Iron Man, and they could exchange technology and strategies.