Another plot twist might be that an enemy disguises itself as Baby Trunks to get close to Bulma. Bulma, being the smart scientist she is, starts to suspect something is off when 'Trunks' shows an unusual interest in her latest invention that has a powerful energy source. This would lead to a cat - and - mouse game between Bulma and the impostor.
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.
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.
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.
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.
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.
One idea could be a time - travel twist. Maybe Bulma discovers a way to travel to a different timeline where Trunks is older and there's a complex relationship that develops between them, full of emotional turmoil and discovery. It could explore themes of love across different versions of themselves.
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.
Some common themes could be family bonds. Since Bulma is Trunks' mother, stories might explore their relationship within the family dynamic. Another theme could be adventure. Given their association with the Dragon Ball universe which is full of action and adventure, fanfics might have them going on quests together. Also, character development is a likely theme, showing how Trunks grows up under Bulma's influence or how Bulma matures as a mother over time.
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.
One idea could be that Trunks discovers a new power while on a mission, and Bulma helps him control it in a unique way. Maybe she creates a device that can enhance his power but also has some unforeseen side effects that lead to some comical and heartwarming moments between them.
One interesting Bulma Trunks fanfic could be the one where Trunks travels back in time and Bulma has to help him adjust to the past without giving away too much about the future. It's full of heartwarming mother - son moments.