Another interesting pairing could be Batman and Daisy Johnson. Daisy has her inhuman powers, especially her seismic abilities. Batman could be intrigued by her powers and try to find ways to use them effectively in combat. And Daisy could learn a lot from Batman's combat training and his no - nonsense attitude towards fighting crime. They could form a strong duo when it comes to facing enemies that require both brute force and strategic thinking.
I think Natasha Romanoff and Melinda May would be an interesting pair. Both are strong, badass women with a lot of combat experience. They could share their stories of their past missions, and also train together. Maybe they could even have a friendly competition to see who is better at hand - to - hand combat or espionage.
One really interesting character pairing could be Fitz - Simmons and the TMNT as a whole. Fitz - Simmons are brilliant scientists, and the turtles are a scientific anomaly. They could study the turtles and their mutagenic origin. The turtles could also benefit from Fitz - Simmons' knowledge of advanced technology. Another pairing that would be cool is Agent Ward (assuming he's not evil in this fanfiction) and Leonardo. Ward is a skilled agent, and Leonardo is a skilled ninja. They could exchange fighting and survival skills, and their different perspectives on loyalty and duty could lead to some interesting story arcs.
Definitely Coulson and Iron Man. Coulson is a big fan of Iron Man in the show, and seeing them interact would be great. Iron Man's sarcasm and Coulson's more straight - laced nature would create some really interesting banter.
I think Daisy Johnson would be really interesting. She has her unique powers and a complex backstory from her time in SHIELD. In a crossover, she could interact with the likes of Thor. Maybe she could learn some new ways to control her powers from him, as he has experience with his own godly powers. And she could also show the Avengers her skills in combat and stealth that she learned in SHIELD. It would be fascinating to see how she holds her own among the super - powerful Avengers.
Daisy Johnson from Agents of Shield would be really interesting. Her own Inhuman powers make her a natural bridge between the two groups. She could help the Inhumans understand the ways of Shield and vice versa. Also, Black Bolt from the Inhumans is fascinating. His power is so extreme that just speaking could cause destruction. How would he interact with the Agents of Shield? What kind of strategies would they have to come up with to communicate with him? It would be really engaging to explore.
I think the interaction between Coulson and Captain America would be really interesting. Coulson is a big fan of Captain America, and Steve would be impressed by Coulson's leadership and the way he holds his team together. They could exchange stories about their different experiences in the war - Steve from World War II and Coulson from more modern conflicts.
I think Makoto Naegi and Robin would make an interesting pair. Makoto represents hope and Robin is always there to support Batman. They could learn from each other's positive outlooks. Also, Kyoko Kirigiri and Batman himself could be a great pairing. Kyoko's detective skills are top - notch, and she could either assist Batman or be a bit of a mystery for him to figure out as she has her own secrets.
Another great pairing could be Rin Tohsaka and the Shield Hero. Rin is a skilled mage in the Fate universe. She could help the Shield Hero understand the magic in the Fate world, and in return, the Shield Hero could show her some of his shield - based techniques that might be useful in combat. Plus, their different personalities would lead to some interesting interactions.
I think the interaction between Bruce Banner and Fitz - Simmons would be fascinating. Fitz - Simmons are brilliant scientists, and Banner is a scientific genius himself. They could collaborate on some new scientific research, like finding a way to control the Hulk better or developing new energy sources. Also, Clint Barton and Skye could have an interesting dynamic. Clint's no - nonsense approach and Skye's hacker - turned - agent background would make for some great banter and teamwork.
Definitely Captain America and Agent Coulson. Captain America represents the old - school heroism of the Avengers and Coulson is the heart and soul of Agents of Shield. Their different leadership styles and moral compasses would create a great dynamic. They could learn from each other, like Coulson teaching Cap about modern technology and Cap teaching Coulson about the values of the past.