Well, you could write a fanfiction where the AllSpark plays a more central role in Darkness Rising. Maybe it has some sort of hidden message or power that the Autobots and Decepticons are unaware of. Another idea is to focus on the relationship between Optimus Prime and Megatron during this time. What if there was a moment where they could have reached an understanding but something got in the way? And for a more character - driven story, you could explore how the events of Darkness Rising affected Bumblebee on an emotional level, and how he grows from it.
One idea could be exploring the backstories of the Decepticons in more detail. For example, how did Starscream become so power - hungry? Another could be creating an alternate timeline where the Autobots lose in Darkness Rising and have to find a new way to fight back. Maybe a story about a human getting caught in the middle of the Autobot - Decepticon war and having to use their wits to survive.
A cool plot for Transformers Prime: Darkness Rising fanfiction could be a story where the Autobots discover a hidden power within themselves that was unlocked during the events of Darkness Rising. This power could change the course of the war. Or perhaps a fanfiction about a Decepticon who has a change of heart and tries to help the Autobots, but has to face the wrath of his former comrades. You could also write about a new character, a young Transformer, who emerges during the chaos of Darkness Rising and has to choose a side.
Another plot could involve a group of characters from different factions in 'the darkness rising' fanfiction having to team up. They might not trust each other at first, but as they face greater threats from the darkness, they learn to work together. For example, a former enemy might have crucial knowledge about a weakness in the dark forces.
One idea could be a story where Optimus Prime has to team up with an unlikely ally from another planet. Maybe a small, scrappy alien that has some unique abilities that can help in the fight against the Decepticons. This would add an interesting dynamic as Optimus has to learn to work with a very different being.
One idea could be exploring the backstory of a minor character in the Darkness Rising Series. Maybe a character who only had a brief appearance but had a lot of potential. For example, you could create a story about how they got involved in the events of the series in the first place.
Another plot idea could be a 'what if' scenario. What if the main character made a different choice at a crucial moment? This could lead to a completely different outcome for the story, like different alliances forming or new threats emerging.
A plot idea could be that Optimus Prime time - travels. He goes back to the beginning of the war between the Autobots and the Decepticons and tries to prevent it from starting. Along the way, he meets younger versions of his friends and enemies and has to deal with the consequences of changing the past. Or perhaps, Optimus is trapped in a dimension where the laws of physics are different. He has to adapt quickly and find a way back to his own world while also facing off against new threats.
Popular characters in Transformers Prime: Darkness Rising fanfiction are often Optimus Prime due to his leadership and moral compass. He's the hero that many stories revolve around. Bumblebee is also highly popular as he represents the connection between the Autobots and humans. His ability to communicate through radio and his loyalty are endearing traits. Megatron is another key character. His tyrannical rule and his thirst for power over the AllSpark make him a great villain. Arcee, with her combat skills and her own backstory, can also be an interesting character to include in fanfiction.
One plot idea could be that Female Optimus Prime has to lead a team of misfit Autobots to save a planet from a new, powerful Decepticon threat. She has to use her unique leadership skills and strength to unite the team.
One idea could be exploring Starscream's origin as a 'baby' in the context of the Transformers Prime universe. Maybe he was created with a special purpose that was later forgotten or corrupted.
There could be a fanfiction where Bumblebee loses his memory. Arcee takes it upon herself to help him regain it. She takes him to all the places they've been together, shares their memories, and tries to jog his memory. As she does this, she also realizes how much Bumblebee means to her and how important their relationship is. This is a story about friendship, loyalty, and the power of memories.
One idea could be an OC who is a medic that gets captured by Megatron. Megatron initially sees the OC as a tool to use against the Autobots but gradually develops an odd respect for the OC's skills and tenacity. Another plot could involve an OC who has a special power that Megatron wants to harness for his own evil plans. As he tries to manipulate the OC, the OC starts to see through his lies and tries to turn the tables on him. A third plot might be an OC from a different dimension who accidentally lands in the Transformers Prime universe and catches Megatron's attention. He's intrigued by this strange new being and tries to either recruit or destroy the OC.