Well, it could be through some heroic actions he takes that showcase his brilliance and courage.
Often, it could be in moments of self-sacrifice or when he uses his tech skills in unexpected and spectacular ways that make the Avengers fully understand his BAMF status in the fanfiction.
Tony Stark could use his intelligence to analyze the BAMF's weaknesses. He might quickly run scans during their encounters to figure out what can harm the BAMF. Then, he could upgrade his Iron Man suit with new weapons and defenses specifically designed to counter the BAMF's attacks.
In a fanfiction, perhaps Nebula saves Tony Stark's life during a space battle. Tony, being the brilliant mind he is, then decides to create a new weapon or technology with Nebula's help. They bond over their shared experiences of survival and their determination to protect the universe. Their relationship could grow from mutual respect to a deep friendship as they face various challenges.
It could bring them closer. By reading and discussing Tony fanfiction, they'll be focusing on a common interest related to one of their own. This shared experience can enhance their sense of unity.
Well, she could have a mentor - mentee relationship with Bruce Banner. He could help her with the scientific aspects of her father's work. And she might be a bit scared of Hulk at first but then realize that he's just as much a part of the team as the others. With Hawkeye, she could learn about precision and focus in combat. Also, she could bring a new dynamic to the group, being the younger and more inexperienced one, but also having fresh ideas and a different perspective based on her unique upbringing as Tony Stark's daughter.
The plot could involve Tony and Nebula going on an adventure to find a powerful energy source that was lost during the events of the Infinity War. Along the way, they encounter various alien species that try to stop them. Tony uses his quick thinking and Nebula her combat skills to fight through. In the end, they find the energy source and use it to power a new device that can protect Earth from future threats.
The Avengers would be in a state of panic and fury. Captain America would likely lead the charge to find Tony. He'd use his military strategy skills to plan a rescue mission. Thor might use his godly powers to track down any signs of Tony's whereabouts. Black Widow and Hawkeye would be on the lookout for any Hydra agents or informants. Hulk could be a wildcard. He might be uncontrollably angry and ready to smash anything in his path to get to Tony.
To write an engaging Avengers Tony Stark OC (Original Character) fanfiction, first, understand Tony Stark's character well. Read the comics and watch the movies to grasp his personality, his wit, his genius, and his flaws. Then, develop your OC carefully. Give them a unique backstory, appearance, and set of skills. For example, your OC could be a brilliant scientist who challenges Tony in the lab, creating interesting dynamics. Next, think about the plot. It could involve a new threat to the Avengers where your OC plays a crucial role. Maybe they have a special ability that helps in defeating the enemy. Also, don't forget to include some great dialogue, especially between Tony and your OC, filled with banter and moments of realization.
It could be interesting because it would force the other Avengers to grow in different ways. They would have to adapt without his resources and skills. This could lead to new friendships and rivalries within the team. Plus, we could see how the Avengers deal with threats without Stark's input, which might involve them using more unconventional methods.
Tony would probably be extremely hurt. He trusted his team, and betrayal would cut deep. He might initially be in denial, not wanting to believe that his friends could turn on him.
In fanfiction, their interactions can also be very tense. Tony might try to use his sarcasm and intelligence to taunt Thanos, while Thanos, with his calm and collected demeanor, would simply brush it off. Sometimes, Thanos might even admire Tony's tenacity in the face of such overwhelming power, which could lead to some interesting exchanges between them.