It could be a new Saiyan character created specifically for the fanfiction. This character could be a strong - willed Saiyan female who has her own set of powers and a unique personality. She might be attracted to Goku because of his strength and his kind heart.
If Goku was a Saiyan in a fanfic, it could explore different aspects of his heritage and potential. Maybe there would be hidden powers or ancestral ties that come into play.
Then, introduce some shared experiences. Maybe they get trapped in a strange dimension together. In this new and dangerous place, they have to rely on each other's strengths. Goku's physical power and Frieza's cunning could be the keys to their survival. As they go through these experiences, they start to see each other in a new light and their relationship begins to change.
One trait is his love for combat. Goku would constantly seek out strong opponents to test his skills. Another is his Saiyan pride. He might not back down from a challenge even if it seems impossible. Also, his Saiyan appetite. He would probably eat huge amounts of food to fuel his Saiyan - level energy.
If Goku married a Saiyan in a fanfiction, it might bring new challenges and adventures. Maybe there'd be family feuds or combined efforts to protect their kind. It really depends on how the author envisions their relationship and the subsequent story arcs.
Well, friendship is also a theme. Despite their differences, they might form an unlikely friendship. In some fanfictions, they learn from each other. Goku might learn about strategy from Fem Frieza, while Fem Frieza could learn about determination and the will to protect from Goku. And of course, adventure is a big theme. They could go on quests together, exploring new planets and facing new challenges.
One common theme is redemption. Frieza is often portrayed as having a chance at redemption through his interactions with Goku. For example, in some fanfics, Goku's unwavering belief in the good in people (or in Frieza's case, beings) starts to make Frieza question his own evil ways.
Well, if Goku was the legendary Super Saiyan in fanfiction, it could completely change the power dynamics in the Dragon Ball universe. There might be new enemies or allies formed based on this twist.
One interesting plot could be Goku and Fem Frieza having to team up against a new, powerful enemy. Maybe this enemy is threatening both of their planets or has some power that neither can defeat alone. Another plot could be Fem Frieza falling in love with Goku and trying to change her evil ways to be with him, but struggling with her past and her reputation among the villains.