Another option is Tumblr. There are many Dragon Ball Z fans on Tumblr who create and share fanfiction. You can search for relevant tags such as '#God of Destruction Goku fanfiction' to find posts related to this topic. However, the content on Tumblr can be a bit more scattered compared to dedicated fanfiction sites.
Vegeta would be a great addition. His rivalry with Goku and his pride as a Saiyan would add an interesting dynamic. He might be initially jealous that Goku is getting to fight and train with the God of Destruction. But then he would also want to prove himself and join in the action. Whis could also be included. His knowledge and calm demeanor could help in situations where the power of Goku and the God of Destruction gets out of hand.
Some Dragon Ball - themed forums also often have sections dedicated to fanfiction. Members share their own works or recommend good ones they've read. For example, the Kanzenshuu forums might have some great Goku and Black Goku fanfiction.
Yes, there are likely some fanfictions with such a concept. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). Just use the relevant keywords in their search bars.
Vegeta could be a great rival. He might see Goku's new position as God of Destruction as another thing Goku has achieved that he hasn't. This could fuel their competitive nature even more.
Goku does reach a state of immense power in the manga that rivals that of a God of Destruction. However, the specific title and all its implications might not be straightforwardly assigned to him. It's a complex development within the story.
Goku becoming a God of Destruction could mean a new look for him. Maybe his Saiyan armor would transform into something more fitting for a god, with a more regal and powerful appearance. His power level would skyrocket, and he could start to have an influence on the balance of the universe. He'd also likely have to deal with other gods, which would lead to some interesting interactions.
One idea could be Goku struggling to adapt to the role of God of Destruction. He's used to being a protector, so having to destroy planets as part of his new duty would create a great internal conflict.
One interesting 'God of Destruction Goku fanfiction' could be where Goku takes on the role of a God of Destruction in a different universe. He might have to deal with new threats and use his Saiyan powers in unique ways. For example, he could face off against an enemy that can manipulate time and space, and Goku has to find a way to overcome this using his God of Destruction powers.
Goku's training would likely involve learning about the history and responsibilities of the Gods of Destruction. He'd need to study under other gods or perhaps even be mentored by Whis or Beerus. This would include not only physical training but also mental and spiritual training. He'd have to learn to balance his newfound destructive power with his natural Saiyan urge to fight and protect. So, his training would be a complex mix of different elements.
Another place to find 'goku dark fanfiction' is on some Dragon Ball - themed forums. There are often sections dedicated to fanfiction where users share their own creations or recommend stories they've read. However, the quality might vary more on forums compared to the larger fanfiction platforms.