Megatron, if he were to interact with Bumblebee in a crossover, it would be full of conflict. Megatron might underestimate Bumblebee at first but then be surprised by his tenacity. He could try to manipulate Bumblebee into turning against the Autobots, using his charm and power to sway him, but Bumblebee would resist.
In a Transformers and Bumblebee crossover fanfiction, Bumblebee could lose his memory and the other Transformers have to help him regain it while also protecting him from the Decepticons who see this as an opportunity to take him out. They go on a journey through different planets and encounter various strange species along the way.
The technology from the Transformers universe would likely have a huge impact on Remnant. The RWBY characters would be amazed by the Autobots' ability to transform and their powerful weapons. The Autobots, in turn, might be intrigued by the concept of Aura and Semblances.
The logical Spock from Star Trek might be fascinated by the Transformers' mechanical nature and try to analyze them. Captain Kirk, on the other hand, would likely be more bold and adventurous in his interactions, perhaps even challenging the Autobots or Decepticons. Optimus Prime would probably see the Star Trek crew as potential allies in the fight for peace and justice, and he would approach them with respect. Megatron, of course, would see them as either threats or potential tools for his own evil plans.
The characters from Fast and Furious would likely be in awe of the Transformers at first. Dom, for example, would probably be initially hesitant but quickly see the potential of teaming up with them. He might try to learn some of their combat moves to use in his own fighting style. Meanwhile, the Autobots like Optimus Prime would be respectful of the humans' skills and courage. Bumblebee could form a special bond with one of the younger members of the Fast and Furious crew, perhaps sharing his love for speed in a unique way.
The Sailor Guardians would likely be initially cautious around the Transformers. Sailor Venus might be the first to approach them, being the more outgoing one. She could try to communicate and find out their intentions. Optimus Prime, on the other hand, would probably be very diplomatic, trying to assure the Sailor Scouts that they mean no harm. The more impulsive Sailor Scouts like Sailor Jupiter might be a bit quicker to jump into action if she feels threatened, while the Autobots like Ratchet would be there to try and defuse the situation.
The Jaeger pilots would likely be in awe of the Transformers at first. They're used to big machines, but the Transformers are something else entirely. The Autobots would probably be friendly and helpful, trying to work with the humans. Optimus Prime could act as a sort of mentor to the pilots, teaching them about honor and sacrifice. The Decepticons, on the other hand, would see the Jaegers as a threat or something to be used for their own gain.
The development of their relationship could be full of twists and turns. Maybe Bumblebee is sent on a mission behind enemy lines and accidentally runs into Blitzwing. Blitzwing could capture Bumblebee, but instead of turning him in, he starts to have conversations with him. Through these conversations, they learn about each other's values and dreams. Blitzwing might start to question his loyalty to the Decepticons while Bumblebee sees that not all Decepticons are completely bad. This could lead to a very unique and evolving relationship between them.
Eren could be really inquisitive about the Transformers' powers. He might try to learn from them how to better use his Titan - shifting abilities. The Autobots, like Bumblebee, would be friendly and try to communicate with the humans in their own way, which could be a bit difficult at first but they would manage.
He might be cautious at first. Vergil is used to dealing with demons and the like, not giant robots. But once he realizes they're not a threat (or if he decides they are an interesting challenge), he could start to communicate. Maybe through some form of telepathy or just by gestures.
The Autobots could see Ben as an interesting new ally. They might be initially cautious, but as they see him use his Omnitrix to transform and fight, they gain respect for his abilities. Ben, on the other hand, would be in awe of the Transformers' size and power. He could learn from them about advanced technology and use that knowledge to upgrade his Omnitrix. The Decepticons would likely see Ben as a threat or a tool to be used. They might try to capture him or the Omnitrix. Ben's alien forms could have different interactions with the Transformers. For example, XLR8 could be used to quickly scout out Decepticon bases, while Diamondhead could provide a strong defense against their attacks.