In a Gohan in High School DxD fanfiction, Gohan could be a special exchange student. He has to balance his studies and his new life in this strange world filled with devils and angels. He might start a martial arts club in the school, which becomes popular. But his real purpose could be to find a way to bring peace between the different factions, using his Saiyan abilities and kind heart.
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.
In Gohan High School DxD fanfiction, there could be a concept of Gohan's academic influence. Gohan is a very intelligent character. He might introduce new scientific ideas or study techniques to the students at the high school in the DxD world. This could lead to different character developments, as some characters might be inspired to pursue knowledge more seriously, and it could also affect the relationships between different factions in the story, as knowledge could be seen as a form of power.
One idea could be that Superman, with his powers, becomes a sort of protector in the High School DxD world. He could use his super strength to stop any over - the - top fights that break out between the different factions. And his heat vision might come in handy when dealing with some of the more dangerous magical threats that lurk in the shadows of the school.
One possible plot could be Sans getting involved in the supernatural battles in the High School DxD universe. Maybe he uses his unique abilities from his original game to help out the main characters in a fight against a powerful enemy. For example, his bone attacks could be a useful addition to the combat arsenal in that world.
A plot could involve the Annihilation Maker creating a device that can enhance or steal the powers of the characters in High School DxD. This device falls into the wrong hands, like a group of rogue exorcists who want to use it to purify all the devils and fallen angels. The main characters then have to race against time to retrieve the device from the exorcists. Along the way, they face many challenges and battles, and the Annihilation Maker has to use their skills to reverse the effects of the device if it has already been used on some of the characters.
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.
One possible plot could be the characters from both series attending a joint high - school event. For example, the Seven Deadly Sins characters could participate in a sports tournament at the High School DxD's school. Meliodas could show off his incredible strength in the athletic events, while Issei from High School DxD might be trying to impress the girls with his newfound powers. This would lead to some friendly rivalries and also some unexpected alliances as they face off against other schools in the tournament.
One possible plot is that Gilgamesh views the High School DxD setting as beneath him at first. But as he gets to know the characters like Issei and Rias, he starts to see the value in their struggles. He could then use his vast resources and power to help them in their fight against stronger enemies, all while maintaining his haughty and kingly demeanor.
One possible interesting plot could be that Naruto, with his unique ninja skills, gets transferred to High School DxD's world. He might initially struggle to adapt to the different rules and magic there. For example, he could mistake a devil's magic for some kind of new jutsu. Then, he could end up teaming with Issei and his group to fight a common enemy that threatens both the ninja world and the world of High School DxD. Maybe an ancient evil that wants to use the power of both chakras and devil magic for its own dark purposes.