Yes, there are some great ones. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Goku Highschool DxD' and you'll find a variety of stories with different plotlines and interpretations.
Well, there are several common themes. First, there's the clash of cultures. Goku comes from a very different background than the characters in Highschool DxD, so how they interact and understand each other is a big part of many stories. Then there's the theme of self - discovery. Goku might discover new aspects of his powers or his personality while in this new world. Additionally, the idea of protecting the new world he's in is also quite common. Since he has a heroic nature, he would likely want to keep the Highschool DxD world safe from any threats, whether they're new to him or familiar from his own universe.
Well, in fanfiction, if Goku Black fuses with Goku, it could result in a super powerful being. Their combined powers might create a new form with an extremely high power level. This new entity could have a mix of Goku Black's dark and devious nature with Goku's pure-hearted heroism, leading to an internal struggle within the fused form.
If Goku Black fuses with Goku in fanfiction, the story would progress in a complex way. The fused form might go on a journey to understand itself. Since it has two very different personalities combined, it would face a lot of internal conflict. This could be used to explore themes like identity and the struggle between good and evil. Externally, the fused Goku could attract new enemies who see it as a threat to their power or plans.
It could be a really exciting story. Goku's godlike powers in the world of Highschool DxD would surely disrupt the power balance. He might introduce new fighting styles and values to the characters in DxD. For example, his Saiyan pride and never - give - up attitude could inspire the devils, angels, and fallen angels in that universe. Maybe he'd end up being a mentor figure to Issei or other main characters, teaching them how to reach new levels of power through training and self - discovery.
Goku would fit in as a super - powerful outsider. His physical strength and combat skills are far beyond what the normal characters in Highschool DxD are used to. He could become a sort of protector for the school, using his powers to fend off any threats that come their way. His energy - sensing ability would give him an edge in detecting hidden enemies.
Another characteristic is the expansion of the Goku Black universe. It could introduce new powers for Goku Black, or new versions of the characters he interacts with. For instance, a fanfiction might give him a new transformation that is unique to that story. The best Goku Black fanfictions also manage to stay true to the essence of his character while still bringing something new and exciting to the table.
One great 'Dragon Ball Goku Black Fanfiction' is 'The Dark Ascension of Goku Black'. It delves deep into Goku Black's psyche and his motives for his actions in a really interesting way. The author does a wonderful job of exploring his character beyond what we saw in the original series.