They could go on a mission to stop a group of tech - thieves. Kid Tony Stark uses his inventions to track the thieves, while the Winter Soldier uses his combat skills to take them down. Another adventure could be exploring an abandoned Hydra base. The Winter Soldier has some knowledge of the layout, and Tony's scientific expertise helps them understand and deal with any hidden traps or dangerous experiments left behind.
In an alternate universe, their interaction could be really interesting. Kid Tony Stark, with his brilliant mind even at a young age, might be both intrigued and a bit intimidated by the Winter Soldier. He'd probably be eager to figure out the technology behind the Winter Soldier's enhancements, while the Winter Soldier could see in Tony a potential for good or bad, depending on how his powers are used. Their dynamic could start off as wary but gradually turn into a begrudging respect as they realize they both have their own moral compasses.
One great fanfiction could be where the Winter Soldier and Tony Stark are forced to team up. In this story, their initial distrust gradually turns into respect as they face a common enemy. They learn from each other's skills, with Tony's tech knowledge and the Winter Soldier's combat abilities complementing each other.
Another theme is the power of technology. Tony is a technological genius, and his tech often comes into play when dealing with Bucky. Sometimes it's about fixing Bucky's arm, other times it's about using tech to help Bucky deal with his mental programming. In some fics, they might even create new tech together, which shows how their skills can combine.
The 'mystery connection' trope is also seen a lot. This is where there is some hidden link between the two characters, like a shared enemy from the past that they don't initially know about. As they uncover this mystery, their relationship evolves and they become closer, whether it's as friends or something more.
One great Tony Stark Winter Soldier fanfiction is 'The Unlikely Alliance'. It shows an interesting scenario where Tony and Bucky have to work together against a common enemy. The story is full of action and also explores their complex relationship.
There are probably some. Fanfiction writers often explore different relationships between characters. You might find some really interesting stories with this pairing. Some could be about their unexpected friendship, or even a more complex emotional bond in an alternate universe scenario.
There's also 'Bucky's Vow'. In this fanfiction, Bucky feels a strong sense of protectiveness towards Tony from the start. It delves deep into their characters, showing how Bucky overcomes his past traumas to be there for Tony. The chemistry between them is really well - written.
One common theme could be redemption. Maybe the Winter Soldier is trying to make up for past actions and forms a bond with Tony during that process. Another might be trust - building as they overcome their initial differences.