Another plot could be that the Dragon Balls are somehow transported to the High School DxD world. This causes a scramble among all the factions in that world to obtain them. Meanwhile, the Z - fighters are also on a quest to retrieve the Dragon Balls. Along the way, they form unexpected alliances with some of the High School DxD characters and face off against common enemies.
One possible plot could be that the characters from Dragon Ball Z end up in the High School DxD world and have to deal with the different power dynamics and social hierarchies there. For example, Goku could be intrigued by the way the devils and angels in High School DxD have their own unique powers and politics. He might try to learn from them while also showing off his Saiyan strength.
One interesting story could be the ones where the characters from Dragon Ball Z end up in the High School DxD universe and have to adapt to its rules. For example, Goku trying to understand the whole devil - angel - human dynamic in the High School DxD world would be quite fascinating.
A third storyline could be about the high school students discovering the Dragon Balls. They might start off thinking they're just some cool artifacts, not realizing their true power. As they start to figure it out, they could get into all sorts of adventures, with the Z - fighters having to step in to protect them from those who would misuse the Dragon Balls.
Goku would be really interesting. His pure - hearted and naive nature would contrast greatly with the more complex and often morally ambiguous characters in High School DxD. He would see the battles and power struggles in a different light, probably just wanting to test his strength and have a good fight without getting too involved in the politics.
One possible plot could be that Thanos somehow gets his hands on the Dragon Balls. He wishes for the power to snap away half of all life in the universe even more easily. The Z - fighters sense this great imbalance and travel to the Marvel universe to stop him. Goku, being the most powerful Z - fighter, tries to fight Thanos but quickly realizes his strength is different from what he's used to. Vegeta might have to team up with Iron Man to come up with a technological way to counter Thanos' Infinity Stones while Goku trains to reach a new level of Super Saiyan to take on Thanos directly.
You can try some popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). They usually have a large collection of fanfictions including those related to Dragon Ball Z and High School DxD.
A possible storyline is the characters forming a high school club related to martial arts or self - defense. They could teach other students and at the same time learn more about human relationships and teamwork. This would be a great way to see how they adapt to normal high school life while still having their unique powers and abilities.
Yes, there are many. You can find them on various fanfiction websites. Some might focus on crossovers between the two universes, like having characters from Dragon Ball attend the high school in DxD. Others could explore unique power combinations or relationships between the characters from both series.
One possible interesting plot could be that Super 17 gains new powers that are not in the original series. Maybe he discovers a hidden energy within himself that allows him to time - travel. This could lead to him trying to change key events in the Dragon Ball Z universe, creating all kinds of chaos and new storylines for the other characters to deal with.
An interesting plot could be that the tournament is secretly organized by an evil force. They have placed a curse on the fighters so that if they lose, they lose their powers forever. Goku and his friends don't realize this at first. As the tournament progresses, they start to notice something is wrong. They have to not only win their battles but also figure out how to break the curse before it's too late.
One idea could be to have the characters from Dragon Ball Z attend the school in Highschool DxD. For example, Goku could be a transfer student with his incredible power causing quite a stir among the devils, angels and fallen angels. He might be confused by the different social dynamics and the whole concept of the supernatural school setting.