Vergil could interact with the Transformers in a very competitive way. Given his pride and his constant pursuit of power, he might see the Transformers' strength and technology as something to overcome. He could challenge them to duels or races, depending on what abilities the Transformers in the fanfiction possess. On the other hand, if he senses they have a common enemy, he could be more collaborative, sharing his combat skills and learning from their technological prowess.
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 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.
Well, Iron Man and Ratchet might start off on the wrong foot. Iron Man, with his cocky attitude, might try to show off his tech to Ratchet, who would be unimpressed and critical of Stark's technology in comparison to Cybertronian tech. But they could later come to respect each other's skills.
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.
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.
Well, Vergil might be initially confused by the large mechanical beings. He could see them as powerful entities worthy of a fight. Maybe he'd try to test his skills against Optimus Prime, thinking it's a new kind of powerful demon.
The interactions would be full of surprises. For example, Hagrid would be absolutely thrilled to see the huge Transformers. He might even try to befriend them and show them around the Forbidden Forest. The Transformers, in turn, could help the wizards in their fight against dark forces. The spells used by the wizards could have unexpected effects on the Transformers. Some spells might work in strange ways, like a levitation spell making a Transformer hover in a very different manner than it was designed to move. And the personalities of the Transformers and the wizards would clash or blend in various ways, creating a rich tapestry of interactions.
The interaction could be really dynamic. The Twins are known for their banter and they might include the fem reader in it. If she's a feisty character, she could give as good as she gets. Maybe they'll have moments where the Twins show off their Transformer abilities to impress her, and she'll respond with her own skills or knowledge. They could also have some misunderstandings at first due to cultural differences, but gradually work through them.