Another plot could involve the exchange of powers. Some characters from High School DxD might gain the ability to use the weapons or powers from Kid Icarus, like the Power of Flight or the use of the Three Sacred Treasures, and they have to learn to control these new powers while dealing with their own high - school - related drama.
One idea could be the characters from Kid Icarus and High School DxD teaming up to fight a common supernatural threat that combines the mythologies of both universes. For example, a demon - angel hybrid that also has ties to the Greek mythology in Kid Icarus.
Maybe Pit from Kid Icarus gets transferred to the school in High School DxD. His angelic nature causes quite a stir among the devils, angels, and fallen angels in the school. He could form an unlikely alliance with Issei to face the challenges that come with this new environment.
Pit from Kid Icarus is very innocent and pure - hearted. He would be quite shocked by the more lust - driven characters in High School DxD like Issei at first. But over time, his positive attitude might influence Issei to be a bit more noble in his pursuits.
A great plot could involve a tournament in the High School DxD world that Gohan participates in. He teams up with some of the characters from that series. His different fighting style and abilities would shock everyone. There could be some sort of mystery or conspiracy behind the tournament as well, and Gohan's integrity and sense of justice would drive him to uncover the truth.
You could do a crossover with 'Sword Art Online'. The virtual reality aspect of SAO could be combined with the supernatural elements of High School DxD. For example, the characters could be trapped in a virtual world that has elements of both worlds, and they have to fight their way out. Issei might have to use his skills in a new digital environment while also dealing with SAO - like challenges.
One idea could be that Naruto is somehow transported to the world of High School DxD. He could use his ninja skills, like shadow clones, in the battles against the devils and fallen angels in that universe. Maybe he'd form an alliance with Issei and his group, teaching them some unique ninja techniques.
One idea could be that Naruto is somehow transported to the world of High School DxD. He could use his ninja skills, like shadow clones, in the battles that take place in the DxD universe. Maybe he'd form an alliance with Issei and his group, and teach them some ninja techniques to fight against the devils and fallen angels.
One idea could be Naruto being summoned into the High School DxD world during a battle. His unique ninja skills would shock the devils and angels in that universe. He might form an unlikely alliance with Issei, perhaps teaching him some ninja techniques in return for learning about the Sacred Gears.
Another possibility is a story where the power - up systems of both Naruto and High School DxD are combined. For example, Naruto could learn about the Boosted Gear and use it in a new form of his Rasengan. Or Issei could gain chakra and learn some basic ninja techniques. This would create an interesting dynamic as they face common enemies.
Well, a cool crossover idea might be the sharing of powers. Imagine if some of the High School DxD characters could learn Naruto's shadow clone jutsu. It would be really useful in battles. Also, the idea of Naruto characters trying to understand the complex social hierarchy in DxD could be very entertaining. They could end up forming alliances in unexpected ways, like the ninjas teaming up with the devils to fight against a powerful demon from Naruto's world that has somehow entered the DxD realm.
A plot could involve the characters from High School DxD mistaking Ben for a new type of devil or supernatural being because of his alien forms. Ben has to navigate this new world while also trying to find a way back home. Meanwhile, the devils in High School DxD might be interested in the technology of the Omnitrix, leading to a conflict where Ben has to protect it from falling into the wrong hands.
One possible interesting plot could be that the Doom Slayer is somehow transported to the world of High School DxD. He could end up at the school as a new student, but his combat skills and his no - nonsense attitude would quickly set him apart. Maybe he gets involved in the battles between the different factions in the DxD world because they mistake his presence for a threat or an opportunity. He might use his arsenal of weapons from Doom to take on the devils, fallen angels and other supernatural beings in the DxD universe in his own unique way.