Definitely Doctor Strange and Loki. Loki is a master of trickery and Doctor Strange is a master of magic. Their interactions would be full of mind games and magic duels. Loki might try to deceive Strange, but Strange would see through his illusions with his magic.
Thor could also be a great character to focus on. He has his Asgardian powers and a different cultural background compared to the others. In a fanfiction with Doctor Strange and the Avengers, he could be the one who has the most trouble understanding Doctor Strange's magic at first. His reactions to the strange magical situations and how he tries to incorporate his own strength and honor into the mix could create some really engaging storylines. Also, his relationship with other Avengers and how it changes with the addition of Doctor Strange's presence could be explored.
I think the Doctor and Tony Stark would be an interesting pairing. They are both highly intelligent and have a knack for getting out of tough situations with their wits. They could bounce ideas off each other regarding technology and science, and probably argue a lot about whose tech is better.
The interaction between Starfire and Beast Boy would be fascinating. Beast Boy can transform into different animals, and Starfire has her own set of superpowers. They could have some really fun and comical moments together, like when Beast Boy turns into a small animal and Starfire is trying to figure out how to communicate with him. Also, they could team up in battles in really creative ways, with Beast Boy using his animal forms to distract enemies while Starfire blasts them with her energy.
The interaction between Robin and Batman would be really interesting. Robin has his own identity with the Teen Titans now, and Batman is his former mentor. There would be a lot of unspoken history and emotions. Batman might be proud of how Robin has grown, but also a bit overprotective. And Robin would be eager to show Batman that he can handle himself without his constant guidance.
Definitely Naruto and Sasuke. In a 'past Naruto meets Boruto' fanfiction, if Sasuke was also involved in the meeting, it would be really cool. Boruto could see the dynamic between his father and Sasuke, two of the most powerful ninjas. He could learn about their past rivalries and how they overcame them to become allies. It would be a great opportunity for Boruto to understand the importance of having a strong bond with your comrades.
I think Kakashi's interaction with Minato would be very interesting. Kakashi was Minato's student. Meeting his sensei again, especially with Team 7 in tow, would bring back a lot of memories. Kakashi could show Minato how he has grown and passed on Minato's teachings. And Minato could give Kakashi some new insights based on his own experiences.
I think Sherlock and Thor could make an interesting pair. Thor is from a different world with a different set of values and powers. Sherlock would be curious about Thor's origin and powers. Thor, on the other hand, might be a bit baffled by Sherlock's deductive reasoning but also respect his intelligence. Their interactions could be full of misunderstandings at first but then develop into a mutual respect as they face a common enemy together. For example, Sherlock could help Thor understand some of the more complex human motives involved in the conflict they are facing, while Thor could show Sherlock some of the magic and power of Asgard.
The interaction between Spider - Man and Iron Man would be really interesting. Iron Man could be like a mentor to Spider - Man, providing him with new and advanced technology for his suit. Spider - Man, on the other hand, could teach Iron Man a thing or two about being a more down - to - earth hero, as he often deals with street - level crime. Their banter would be great, with Iron Man making sarcastic remarks and Spider - Man coming back with his quick - witted responses.
Rin and Snape would also make an interesting pair. Snape is this brooding and complex character. Rin might initially be put off by his cold exterior but as she gets to know him, she could understand his pain and the reasons behind his actions. And Snape would be curious about Rin's magic which is so different from what he's used to. They could have some tense but also very thought - provoking exchanges.
Definitely Garfield and Leon. Leon is such a strong and respected trainer in Pokemon Sword and Shield. Garfield, on the other hand, is this lazy cat. The contrast between their personalities would make for an interesting interaction. Leon might be really confused by Garfield's lack of interest in becoming a great trainer and just his focus on food.