One idea could be a story where Bulma invents a new device to help Baby Trunks train more effectively. For example, she creates a gravity simulator that allows him to train in conditions similar to different planets.
One idea could be a story about Bulma's inventions and how Baby Trunks gets involved in her experiments. For example, he could accidentally activate a device that sends them on an adventure through time or to a different dimension.
In a fanfiction, there could be a story where an enemy specifically targets Baby Trunks because of his Saiyan heritage. Bulma steps up as his protector, using her inventions to fend off the attacks. Along the way, they develop a stronger bond as they face this common threat together. Bulma also discovers new aspects of her own strength and courage in protecting Baby Trunks.
Their relationships are often shown as loving yet complex. Vegeta, who was once a cold - hearted warrior, has a soft spot for his family. He is protective of Bulma and Baby Trunks. Bulma is the brains of the family, and she manages to keep Vegeta in check. Baby Trunks is the source of joy and also a reason for Vegeta to strive to be a better person.
Fanfiction can explore their relationship by looking at their cultural differences. Vegeta is a Saiyan from a warrior race, while Bulma is a human scientist. Baby Trunks is a mix of both. So, a story could be about how they teach Trunks about his dual heritage, like Vegeta teaching him about Saiyan pride and Bulma teaching him about human values like kindness and curiosity.
A fanfiction could focus on a day in the life of the family. Bulma could be working on some new invention in her lab, Vegeta is training hard outside, and Baby Trunks is getting into all sorts of cute mischief. Then, something unexpected like a small alien invasion occurs near their home, and they all have to work together to deal with it.
A great plot twist could be that Baby Trunks is actually from an alternate future where things are very different. This would change the whole dynamic of how Bulma relates to him. Maybe in this future, Bulma didn't survive, and now he has come back to change the past.
I'm not really into that kind of lemon - filled fanfiction. However, generally, such fanfictions might explore a more romantic or even spicy relationship between Trunks and Bulma. But it's important to note that a lot of this type of content might not be in line with the original spirit of the Dragon Ball series.
A really interesting plot could be that an old enemy of Vegeta's resurfaces and targets Baby Trunks. Vegeta is determined to protect his son at all costs. Bulma, on the other hand, uses her intelligence to come up with a plan to defeat the enemy. There could be a lot of action scenes with Vegeta fighting, and also some heart - warming moments between the family members as they support each other through the crisis.
The story could explore how the news of Bulma's pregnancy affects their friends and family. Goku might be excited to have another Saiyan baby around, and Chi - Chi could offer Bulma some advice on pregnancy. Meanwhile, the Z - Fighters might be on high alert, fearing that the pregnancy could attract the attention of villains who would want to harm Bulma or the unborn child.