It could be Percy and Black Widow. Natasha is a master of reading people, and she'd notice Percy right away. She might approach him in a more stealthy way compared to the others, trying to assess if he's a threat or an ally. And Percy, being used to danger, would be on his guard at first, but then start to trust her as she shows her good intentions.
Probably Ash and Iron Man. Iron Man is always curious about new things and Ash with his Pokémon would be quite an interesting sight for him. He'd likely approach Ash first to ask questions about what he is and what those strange creatures are.
Hulk might be an interesting one too. Sonic's speed could either annoy or amuse Hulk. If they end up on the same side, Sonic could use his speed to lead Hulk towards the enemies. And Hulk's raw strength could be something Sonic would be in awe of. They could have a really unique dynamic, like a fast - moving pest annoying a big, strong giant at first, but then they become an effective team.
Obviously, Peggy and the Avengers are the key characters. Among the Avengers, Captain America would be a central figure in the interaction as he and Peggy have a pre - existing relationship.
Doctor Strange and Ajak. Doctor Strange is well - versed in the mystic arts and Ajak has a lot of knowledge about the Eternals' history and their connection to the Celestials. Their knowledge areas could intersect, and they would likely be the first to start sharing information. Maybe Strange senses some strange energy related to the Eternals and approaches Ajak to find out more.
Probably Harry Potter and Edward Cullen. Since Edward is sort of the main character among the Cullens in a way, and Harry is the central figure in his world. They both have unique abilities and a sense of responsibility, so it makes sense for them to be the first to cross paths and start interacting.
Applejack and the Heavy might be the first to interact. Applejack is a hard - working and practical character. The Heavy is a no - nonsense fighter. Applejack might see the Heavy and be curious about his large size and strange weapon. The Heavy, on the other hand, might be interested in Applejack's farming skills and the fresh apples she might be carrying. Their down - to - earth personalities could lead to an initial interaction.
In this fanfiction, Penny Parker would surely interact with Thor. Thor could share his stories of Asgard with her, and Penny might be in awe of his godly powers. Also, Hulk could be an interesting character for her to meet. Maybe she'd try to find a way to calm the Hulk down when he gets angry. And Black Widow would be another key character. Black Widow could train Penny in espionage and hand - to - hand combat skills.
Death from DarkSiders and Black Widow could have an interesting interaction. Death has seen countless deaths and has a very different perspective on life and death compared to the human Black Widow. Their conversations could be deep and thought - provoking as they work together on a mission.
Probably Goku and Twilight Sparkle. Twilight is the smart and curious one. She would be the first to approach Goku out of scientific interest, wanting to understand where he came from and what his powers are all about.
Probably Naruto and Robin. Robin is the leader - type in Young Justice, always thinking and strategizing. When Naruto shows up, Robin would be the one to approach him first, trying to figure out who he is and what his intentions are. Naruto, being friendly and curious, would be open to the interaction.