Trunks would also be interested. He has his own experiences with fighting powerful foes and would be eager to see how Goku, a great Saiyan warrior, fares against Frieza. Also, the younger Saiyans like Goten might be interested. They've heard stories about Frieza and would be excited to see their father or other Saiyan heroes in action against such a notorious villain.
Broly could be an interesting Saiyan to watch the fight in fanfictions. Given his raw power and his complex relationship with Goku, seeing Goku battle Frieza could trigger different emotions in him. He might be envious of Goku's power, or he could gain some new understanding of combat strategy by observing the fight.
A possible fanfiction could focus on a group of Saiyans who are trapped in a dimension where they can only watch the Goku vs Frieza fight on repeat. They start to notice small details in the fight that they hadn't before, like the exact moment Goku's power level spikes or how Frieza is trying to adapt his strategy. This newfound knowledge could then be used by them in some way when they eventually break free from that dimension.
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.
Issei would be very likely. Since Issei is the main character in DxD, his curiosity and his own pursuit of power would make him interested in Goku. They could train together and learn from each other's abilities. Also, Rias would interact with Goku. As a powerful devil, she would be intrigued by Goku's power and his different way of approaching battles.
Honestly, the best writers are the ones who can take the basic concepts of Goku and Fem Frieza and turn them into something completely different yet still in - character. Some writers do this by exploring different genres within the fanfiction. So instead of just an action - packed story, they might write a romantic comedy or a mystery involving Goku and Fem Frieza. These writers are often the ones who can surprise readers with their creativity and fresh perspectives.
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 likely narrator could be one of Epsilon's closest comrades. For example, if it was someone like Church, who had a deep connection with Epsilon, they could be narrating their thoughts and feelings during and after his death. This would give an insider's perspective on the loss and the significance of Epsilon's role.
Sasuke could also oppose Black Goku. With his Sharingan and Rinnegan, Sasuke has a wide range of powerful abilities. He is also very intelligent and strategic. Sasuke would likely see Black Goku as a threat to the balance of power in the Naruto universe and would step in to fight him, especially if it involved protecting his friends or the ninja world in general.
Goku would be more likely. He is always open to new friendships and challenges. He has a curious nature and would be intrigued by Kefla's power. So he might approach her first to test her strength or just out of friendly curiosity.
Nora could also be a likely candidate. She's very energetic and not one to be intimidated easily. When she sees Goku's amazing power, she would probably be excited and want to team up with him right away. She would be constantly asking Goku about his world and his powers, and they would bond over their love for combat and having a good time.
It's hard to say. Naruto has his powerful Nine - Tails Chakra and Sage Mode. But the five kages are also very strong. However, Naruto has a habit of coming out on top in tough situations, so he might be the likely winner.