Maybe a story where a character from RWBY discovers a lost Transformer in the wilderness. This Transformer could be damaged and in need of repair. The RWBY character, with their unique skills, tries to help the Transformer while also learning about its origin and the greater universe it comes from. This could lead to a deep friendship and an exchange of knowledge between the two different worlds.
One idea could be a crossover where the Autobots from Transformers Prime end up in the world of RWBY. They could team up with the RWBY characters to fight a common enemy, like a new type of Grimm that has some technological abilities similar to the Decepticons. The Autobots' advanced weaponry and technology would be a great addition to the RWBY universe's combat.
One idea could be a human character who discovers a hidden power within themselves that can interact with the Cybertronian technology in unique ways. For example, they might be able to heal damaged Transformers using a special energy they possess.
One idea could be exploring Predaking's origin in more depth. Maybe he has memories from before his creation that he slowly uncovers. Another could be a story where Predaking tries to form an alliance with the Autobots against a common enemy, like a new and powerful Decepticon threat.
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.
Maybe the Transformers end up in Remnant due to a space - time rift. The Grimm might be attracted to the Energon that the Transformers carry. The RWBY teams would have to team up with the Transformers to fight off both the Grimm and the Decepticons if they also show up. Yang could learn some combat moves from the Autobots, which would add a new dimension to her brawler style.
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.
A plot could involve Bumblebee getting damaged and losing his memory. The RWBY characters find him and try to repair him while also helping him regain his memories. As they do this, they learn about the Transformers universe and Bumblebee starts to adapt to the RWBY world, eventually using his unique abilities to help them in a big battle against a powerful Grimm horde and a new villain that has emerged.
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.
You could write a story about a young Autobot or Decepticon who gets stranded in the Beast Wars era and has to learn how to survive among the Maximal and Predacon factions. They might have to adapt to the different rules and cultures while also trying to find a way back to their own time.
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.