Baby Trunks might learn to walk in the fanfic by imitating others or having a sudden burst of determination. It could also be that he gets inspired by seeing his older siblings walk freely and decides to give it a go himself.
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.
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.
In some fanfictions, Naruto might learn this through some magical or spiritual means. But it really depends on the author's imagination.
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.
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.
They could start by having a common goal, like protecting a certain planet or a group of people. This shared objective would make them interact more often and gradually understand each other better.
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.
Well, his friends might rally around him. Hermione would probably start researching every possible spell or potion to help him. Ron, on the other hand, would be there to offer moral support and practical help like getting Harry around. For instance, he could use a levitation charm to move Harry from place to place.
You need to do a lot of research. Watch Dragon Ball Z to fully grasp Future Trunks' character traits and his world. And of course, be familiar with the MLP series. When writing, focus on the character development. Let the two different sets of characters grow and change as they interact with each other. Maybe Trunks becomes more in touch with his softer side through the influence of the ponies, and the ponies become more confident in facing danger because of Trunks.
Well, in certain fanfics, Naruto learns from Kyuubi in a rather interesting way. Kyuubi could show Naruto memories of past battles it was involved in. Through these memories, Naruto can pick up on different fighting styles and techniques. Also, Kyuubi might teach Naruto how to better access and utilize the power of the Nine - Tails chakra, which could involve things like suppressing the negative side effects and maximizing the positive boosts to his strength and speed.