Well, it depends on what you consider 'good'. There are some that focus on adventure scenarios where Optimus and Sentinel have to work together against a common foe. These often explore their different personalities and how they complement or clash with each other. Some other fanfics might delve into their pasts and how that has shaped their relationship in the present. So, it really varies based on your taste.
One possible fanfiction could be about Sentinel Prime and Optimus Prime having to work together to save Cybertron from a new, powerful enemy. They might start off with some differences in their approaches but gradually learn to combine their strengths.
One common theme is friendship. Despite their differences, they often come to understand and support each other more deeply. Another is rivalry, as Sentinel can be quite competitive with Optimus. And there's also the theme of growth, where both characters develop in some way through their relationship.
A plotline could be Sentinel Prime getting corrupted by dark energy and Optimus Prime having to fight him to bring him back to the light. It would be a battle of wills and also a test of their long - standing friendship.
One common theme is redemption. Sentinel Prime, who has made mistakes in the past, might find redemption through his interactions with Bulkhead. For instance, Bulkhead's pure - hearted nature could inspire Sentinel Prime to become a better mech.
One great fanfiction could be about Sentinel Prime and Bulkhead having to team up during a crisis on Cybertron. In this story, Sentinel Prime might initially be reluctant to work with Bulkhead because of their differences in approach. But as the situation worsens, they start to understand and respect each other's strengths. For example, Bulkhead's brute strength and Sentinel Prime's strategic mind could combine to defeat a powerful enemy that neither could have faced alone.
One plot idea could be that Megatron and Optimus Prime are forced to team up in an alternate dimension. They have to put aside their differences to face a common enemy that is threatening the very fabric of that dimension. Maybe it's an ancient evil that has the power to destroy all Cybertronians.
You can try looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. These platforms usually have a large collection of Transformers fanfictions, including those featuring TFA Ultra Magnus and Optimus Prime.
Some fanfictions also explore the idea of self - discovery. Optimus Prime is still growing and learning about his role. Ultra Magnus, with his experience, can play a role in this journey. It could be about Optimus Prime realizing his true potential with Ultra Magnus' guidance, or both of them learning new things about themselves through their interactions.
In a unique way, their relationship could be developed if they were both trapped in a virtual reality world created by an unknown force. In this world, they have to rely on each other's skills to survive and escape. As they work together, they start to respect each other's abilities more and their relationship changes. They might not become friends, but they would have a different kind of understanding.