Maybe there could be a story where the magic system of Black Clover is introduced to the Highschool DxD universe. The devils in Highschool DxD might be intrigued by the concept of mana and the grimoires in Black Clover. The characters could exchange knowledge and abilities. For instance, some of the devils could try to obtain grimoires, leading to a whole new set of adventures and power struggles.
One possible plot could be Naruto being somehow transported to the world of Highschool DxD. He could use his ninja skills and chakra in the battles against the devils and fallen angels in that world. Maybe he teams up with Issei and his group, and Naruto's unique jutsus like Rasengan and Shadow Clone Jutsu surprise everyone.
In a 'Naruto x Kuroka Highschool DxD' fanfiction, the plot could be that Naruto is on a mission to find a powerful artifact that has been lost in the DxD world. Kuroka, being a local with knowledge of the hidden places, offers to help him. Along the way, they discover that there is a conspiracy to use the artifact to take over the school. They must race against time to stop the villains. Naruto's determination and Kuroka's slyness work well together as they outwit the bad guys.
One interesting plot could be Naruto being summoned to the world of Highschool DxD. His unique ninja skills and chakra would be a huge shock to the devils, angels, and fallen angels in that world. He could end up forming an unlikely alliance with Issei, perhaps teaching him some of his ninja techniques in exchange for learning about the Sacred Gears. They could then face a common enemy together, like a powerful devil who wants to use Naruto's power for his own evil plans.
A plot could revolve around Naruto attending Highschool DxD as an exchange student. He would be the odd one out, with his orange jumpsuit and headband. The students at the school would be curious about his powers and his world. Naruto could end up in a love triangle between a devil girl and an angel girl, just like Issei often finds himself in romantic entanglements. He would have to navigate the complex social and power dynamics of the school while still staying true to his ninja way.
Well, a plot could involve Broly being part of a special program in the Highschool DxD setting. He might be there to learn about controlling his power in a more civilized way. As he tries to fit in, he could befriend some of the main characters from DxD. For example, he could team up with Issei and his friends to compete in some sort of school tournament that has magical and combat elements. This would lead to some epic battles and also some character development for Broly as he learns about friendship and cooperation.
Maybe Spider - Man's identity is mistaken in the Highschool DxD world. The characters might think he is some sort of new supernatural being. This could lead to a series of comical misunderstandings as he tries to explain his powers and where he comes from while also dealing with the various power struggles and intrigues in the Highschool DxD universe.
Well, in a 'Naruto x Greyfia Highschool DxD' fanfiction, perhaps Naruto is a new transfer student in the Highschool DxD. Greyfia could be a popular student there. Naruto's positive and energetic attitude might attract Greyfia's attention. They could start off as friends and gradually develop a deeper relationship. Maybe they get involved in the supernatural battles of the DxD world together, with Naruto using his Rasengan and other jutsu while Greyfia uses her demonic powers. And as they spend more time together, they learn from each other's worlds and values.
One possible plot could be that Naruto is somehow transported to the Highschool DxD universe and meets Gabriel. They might team up to face a common threat that is endangering both the ninja world and the supernatural world of Highschool DxD. Naruto's unique skills as a ninja could be combined with Gabriel's angelic powers in an epic battle against evil forces.
Well, one possible plot could be that Natsu is betrayed in his own world and somehow ends up in the DxD Highschool universe. Maybe he has to deal with the different power dynamics and politics there while also trying to figure out who betrayed him in his original world. He might form new alliances with the characters in DxD Highschool and use his unique abilities to survive and seek revenge for his betrayal.
One possible plot could be that Naruto, with his godlike powers, ends up in the world of Highschool DxD. He might join the Occult Research Club and use his unique abilities to protect the club from various threats. His ninja skills and super - powered jutsus could be a huge asset in battles against devils, fallen angels, and other supernatural foes.