In the fanfiction, it could be that there was some sort of mission or adventure that brought the three together. During that time, the relationship developed and the girl got pregnant. Steve and Bucky might then use their skills and resources to protect the girl and prepare for the baby. They could have to deal with enemies who might want to harm the girl because of the baby or their relationship.
It could also be strained. There might be some jealousy or differences in opinion on how to handle the situation. For example, one of them might want to be more involved with the girl during the pregnancy while the other feels left out, which could cause some tension between them.
The plot could start with Steve realizing that his bond with Bucky is stronger than his relationship with Tony. Maybe there have been some misunderstandings or conflicts between Steve and Tony that make Steve reevaluate his feelings. Then, Steve decides to break things off with Tony in a rather dramatic way. After that, it could explore how Tony reacts to this rejection, and how Bucky fits into the new dynamic between Steve and the rest of the Avengers.
In this type of fanfiction, it could start with Steve and Nancy having a night of passion and then finding out they're pregnant. They may be in a relationship that was a bit rocky before, but the pregnancy forces them to re - evaluate everything. They might start going to doctor's appointments together and learning about what it means to be parents - to - be. There could be some conflict, like Steve's parents not being happy with the situation or Nancy having doubts about whether she's ready to be a mother so young. But through it all, they could grow closer as a couple and start preparing for their new life together.
One possible plot could be that they have a small, intimate wedding on a beach. All their close friends and family are there. Steve might be nervous at first but seeing Catherine walk down the aisle makes him feel calm and full of love.
Well, they might be really surprised. Some of them could be confused at first. Tony might make a snarky comment like 'What's going on here, boys?'. Natasha would probably just raise an eyebrow and wait for an explanation. And Thor might not fully understand the situation but would try to lighten the mood with a joke.
In this fanfiction, perhaps Steve and Bucky come across Tony when he's being bullied in school for being a genius. They see his potential but also his vulnerability. So, they adopt him. As time passes, Tony starts to show an interest in Steve's shield and Bucky's combat skills. They encourage his inquisitive nature. Steve cooks for them all, creating a homey atmosphere. Bucky teaches Tony how to deal with nightmares as he has his own experiences. And Tony, in turn, uses his intelligence to improve their living situation and help them in their own missions in some way.
On the other hand, Steve might be more understanding than expected. He knows about Bucky's past traumas and could suspect that something else is at play. So, instead of immediately resisting, he might play along for a while, waiting for the right moment to figure out what's really going on and how to help Bucky.
It could be about an adventure they have on the plane. Maybe they are on a mission and face some challenges together, like dealing with bad guys or handling a malfunction on the plane.
Well, it could be about a situation where Steve is carrying Bucky, perhaps in a rescue mission. Steve might be struggling because Bucky is, as the title says, heavy. Maybe Bucky is injured and Steve has to carry him to safety, and the story could focus on Steve's determination and their friendship during this tough situation.
One possible plot twist could be that Bucky and Steve initially protect Tony out of duty, but then they discover a deeper connection between them all. Maybe they find out that Tony has been unknowingly targeted by a common enemy from their past. Another plot twist could be that while protecting Tony, they accidentally expose a secret of Tony's that he was trying to keep hidden, which then leads to a whole new set of challenges for all of them. It could also be that the way they protect Tony causes a rift in the superhero community, as some might think they are being too overprotective or that Tony doesn't deserve such protection.