Goku's reaction could be a mix of shock and joy. On one hand, he has been on Earth for so long without any real family connection to his Saiyan side. When he sees his parents, it would be overwhelming. He would likely be in awe of his father, Bardock, given his father's reputation as a strong Saiyan. And he would be eager to bond with his mother, who he has never known. He might also feel a sense of belonging that he has been missing all his life.
Goku's understanding of different universes and races could be deepened in fanfiction. Since Dragon Ball Super introduced the multiverse concept, fanfiction could explore how Goku interacts with and learns from beings from other universes, making him more worldly and less naive in some ways.
One of the interesting power - ups could be his Ultra Instinct form. In fanfiction, it might be further enhanced, like having different levels that are not shown in the original. For example, he could have an Ultra Instinct - Kaioken combination which would be extremely powerful.
A fanfiction might explore the idea of Bardock seeing Goku's life through a time - space rift. He witnesses all of Goku's battles and the friends he makes. Bardock is filled with pride but also realizes that Goku has a different path than the traditional Saiyan way. This makes him question the Saiyan culture he once knew. Meanwhile, Goku starts to have strange dreams about his father, which leads him to search for more about his Saiyan heritage.
One possible fanfic could be about Bulma and Young Goku's first adventure together. It might start with Bulma recruiting Goku to find the Dragon Balls. They could face various challenges like wild animals and bad guys along the way. Their different personalities, with Bulma being smart and resourceful and Goku being naive but strong, would create interesting interactions.
One great 'Dragon Ball Goku Black Fanfiction' is 'The Dark Ascension of Goku Black'. It delves deep into Goku Black's psyche and his motives for his actions in a really interesting way. The author does a wonderful job of exploring his character beyond what we saw in the original series.
Yes. Goku is one of the most powerful characters in Dragon Ball. He has achieved various powerful forms like Super Saiyan God, Ultra Instinct, etc. With his constantly growing power, he is capable of taking on almost any threat within the Dragon Ball fiction. There are very few characters that could potentially rival him, and even then, he usually finds a way to overcome them.
There isn't really a love story between them. Goku is more focused on his family in a different way and his pursuit of getting stronger. Vegeta also has his own pride and family with Bulma. Their bond is more of a friendship that developed through countless battles and challenges together.