I'm not sure who Tony specifically is in this fanfiction without reading it. It could be an original character created by the author, or perhaps a reimagined version of a known character in a particular fictional universe.
I don't have enough information to know exactly who Tony Yamazaki is in this context. He could be an ordinary person with an extraordinary story, or he might be someone known in a particular community or industry.
Tony could be the team captain. As the captain, he has a special bond with the team members and might want to do something special to boost their morale. He would know what kind of surprises would really make an impact on them.
In most kerry and tony fanfiction, Kerry is often depicted as brave. For example, in many stories, Kerry is the first to face challenges. Tony, on the other hand, is usually more of a thinker. He comes up with plans to solve the problems they encounter.
In this fanfiction, Tony might also meet Loki. Loki could be either a friend or a foe to Tony. He might try to trick Tony for his own amusement or they could end up working together against a common threat to Asgard.
Tony would likely be defiant. He's not the type to cower in the face of danger. He might immediately start looking for weaknesses in Thanos' setup and try to escape on his own terms.
Well, in the 'Avengers Tony is a God' fanfictions, Tony's character evolution is really interesting. His technological prowess is often magnified to a god - like level. For example, he could have the power to create and manipulate matter at will. This not only changes his relationship with his fellow Avengers but also how he views himself. He may struggle with the newfound power and the responsibility that comes with it, just like in the original stories but on a much grander scale.
One great 'Bucky x Tony Tony nightmare' fanfiction is 'The Broken Alliance'. It delves deep into the complex relationship between Bucky and Tony. In this story, a nightmare situation forces them to confront their past differences and work together. The character development is really well - done, showing how they grow from being at odds to understanding each other on a deeper level.