It could lead to an incredibly powerful character with a mix of Buu's elasticity and Gohan's potential. Maybe they'd have new abilities and face even greater challenges.
In some fanfictions, Gohan and Goku might have a series of conversations that open up new levels of understanding between them. Gohan could share his thoughts and feelings about his life and future, and Goku would listen and offer his own insights. This kind of communication can really strengthen their bond.
In such fanfictions, Goku might develop by becoming more of a mentor to Gohan. He could teach Gohan new fighting moves and also how to control his emotions better during battles.
In a Gohan x Goku fanfic, their relationship can be delved into by creating scenarios where they have to rely on each other completely. For example, if they are in a situation where Goku's strength and Gohan's intelligence are both required to escape. Their different personalities can also be highlighted. Goku's carefree nature contrasted with Gohan's more studious and responsible side. And of course, flashbacks to Gohan's childhood and how Goku's presence or absence affected him can add depth to their relationship.
One possible interaction is that Bardock could spar with Goku and Gohan. He'd test their limits and see how much they've learned about fighting. Another could be Bardock sharing stories of Planet Vegeta with them, which would be really interesting for Goku and Gohan to hear.
I found a fanfiction that focuses on Female Majin Buu's growth as a character with Gohan as her mentor. It's interesting because it delves into how she adapts to life on Earth with Gohan's guidance. The story also has some really cool action scenes where Gohan and Female Majin Buu train together and then use their combined skills to take on villains.
In the manga, Gohan never managed to defeat Goku. Their battles often ended with Goku coming out on top or the fight being interrupted for some reason.
A common theme is the power dynamic. Gohan is a powerful Saiyan, but Female Majin Buu has her own unique abilities. Their relationship often explores how they balance and combine their powers. Another theme is friendship. They come from very different backgrounds, so the fanfictions usually show how they overcome those differences to become friends.
In many fanfictions, Goku's protectiveness of Gohan is shown through his constant presence. He might train Gohan more rigorously to make him stronger so he can defend himself. For example, in some stories, Goku takes Gohan to special training grounds that are hidden from the rest of the world. This not only protects Gohan from potential threats during the training but also hones his skills in a more secluded environment.