Maybe in this fanfiction, Goku realizes that he and Chi - Chi have very different personalities. Chi - Chi is often more concerned with family and a stable life, while Goku is a free - spirited adventurer. This clash of values could lead him to decide not to marry her. For example, Chi - Chi may want Goku to stay at home and help raise Gohan, but Goku is eager to explore new planets and fight powerful enemies.
Some people might create it just for shock value. They know that the original relationship between Goku and Chi - Chi is loving, so by creating something so opposite, they can get a reaction from readers.
One reason could be his pursuit of stronger opponents. Goku is always eager to test his strength and find new challenges. In fanfiction, this might lead him to leave Chi - Chi to travel the universe in search of the toughest foes. He might feel that staying at home with his family restricts his growth as a fighter.
In this fanfiction, the story could develop in a way that Goku's decision not to marry Chi - Chi has a ripple effect on the entire Dragon Ball universe. His friends might be shocked and try to persuade him otherwise. But Goku stands his ground. This could lead to new alliances being formed as some characters side with Goku's decision, while others support Chi - Chi. The lack of the Goku - Chi - Chi marriage also means that Gohan's upbringing is different. He may grow up with a stronger sense of independence, seeing his mother as a sole provider, and this could influence his future actions and development as a fighter.
A third possible plot is that Goku and Chi - Chi meet in a parallel universe where their relationship is completely different. They could explore this new dynamic and learn from each other. Maybe in this universe, Chi - Chi is a powerful warrior herself, and they team up to fight a common enemy, which changes their relationship in their own universe when they return.
One reason could be to explore a completely different side of the characters. Maybe the writer wants to see how the Dragon Ball universe would react to such a scandal. Another reason might be for shock value, to get readers' attention with a very unexpected plot twist.
I'm not sure if there is an actual fanfic with that exact plot. Fanfic topics can vary widely, but this seems like a rather unfaithful and out - of - character concept considering Chi Chi's strong bond with Goku in the original series.
Maybe Videl. She's strong - willed and also into martial arts. They could have met in a different way and their shared interest in fighting could have led to a romantic connection. However, this would change a lot of the existing storylines.
Love and family are very common themes. Their relationship as husband and wife, and as parents to Gohan and other children is often explored.
In the manga, Goku and Chi Chi have a complex relationship. They start as childhood friends and later get married and have kids. Their relationship has its ups and downs, but they always care for each other.
The 'Goku Chi Chi Sex Comic' is a form of inappropriate and disrespectful material. It strays far from the intended themes and messages of the original works and can have negative impacts on the perception of the characters and the franchise as a whole.