A really interesting plot could be about Baby Starscream getting a glimpse into a possible future where he becomes a powerful and feared Decepticon. He could then be conflicted about whether to follow that path or try to change his destiny. This would involve a lot of internal struggle and self - discovery for his character.
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.
The sparkling could be a prophesied figure in Cybertronian lore. Starscream, believing in the prophecy, decides to side with the sparkling instead of his usual self - centered ways. He has to protect the sparkling from both Autobots and Decepticons who don't believe in the prophecy or want to use the sparkling for their own ends. This plot would involve a lot of action and moral dilemmas for Starscream.
You can try looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. They have a large collection of Transformers fanfictions, and there's a good chance you'll find some related to Baby Starscream there.
One plot idea could be that Optimus Prime and Starscream are forced to team up during a crisis that threatens both Autobots and Decepticons. They start to see each other in a new light and develop an unlikely friendship. Another could be a story where Starscream is injured and Optimus Prime has to make the choice between helping him or leaving him to the mercy of other Decepticons. This could lead to a complex relationship between them. A third idea is a time - travel plot where they end up in an alternate universe where their roles are reversed and they have to figure out how to get back to their own universe while dealing with their changed relationship.
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.
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.
In a fanfiction, Starscream might be in a situation where he has to protect a sparkling from other Decepticons who see it as a threat or a nuisance. Starscream, known for his self - serving nature, could struggle between his usual motives and this newfound sense of responsibility towards the sparkling. This internal conflict could lead to a lot of character development for him.
There's a fanfiction called 'Starscream's Ascent'. In this story, Starscream discovers a hidden power within himself. The author does a wonderful job of portraying his complex personality as he tries to use this new power to gain respect among the Decepticons. It's full of action and his scheming, which is typical of Starscream.
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.
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.