One idea could be a new student arriving at the school who has a unique power that catches the attention of the main characters. For example, a girl from a far - off land who can manipulate time in small ways. This could lead to adventures where they have to fix time - related mishaps in the school. Another plot could involve a love triangle between a human student, a devil, and an angel, all trying to navigate their feelings while also dealing with the politics of the three factions in the Highschool DxD universe. Maybe there could be a school event like a tournament where the characters team up in unexpected combinations to compete, and during this time, romantic feelings start to develop.
A plot could center around a mystery that is plaguing the school. The characters suspect it has something to do with an ancient artifact hidden on campus. As they search for clues, a budding romance could form between an unlikely pair, like a shy devil and an over - confident human. They might start off bickering but as they work together to solve the mystery, they fall in love. Or perhaps a character gets cursed and starts to forget their memories, including their feelings for their love interest. The others then have to find a way to break the curse and in the process, we see different sides of their relationships and the world of Highschool DxD.
One plot idea could be Asia and Gasper teaming up to solve a mystery within the school. Maybe there are strange disappearances and they use their unique abilities to figure out what's going on. Another idea is a story where they go on a journey to find a magical artifact that can help protect their friends. And a third could be a slice - of - life story where they help each other deal with personal problems like Gasper's shyness and Asia's insecurities about her new life in the supernatural world.
For a fanfiction with Issei and Asia married, a great plot could be that Asia discovers a new power within herself after getting married. This power could be related to their combined love and it attracts the attention of an ancient and evil force. Issei then has to train Asia to control this power while also protecting her from the approaching danger. Or perhaps they are chosen to represent their respective groups in a tournament that has high stakes for the future of their relationship and the groups they belong to.
Perhaps a plot where a pregnancy occurs as a result of some sort of magical or supernatural accident in the Highschool DxD world. The story could then focus on the search for a way to reverse it or deal with it. Along the way, the characters might discover new powers or secrets about their world. And the relationships between the characters could be tested as they face this difficult situation together.
One idea could be a gamer who gets transported into the Highschool DxD world and uses his gaming skills to gain power and allies. For example, his knowledge of strategy games helps him in battles and political maneuvering within the devil, angel and fallen angel factions.
Another plot idea could be that the gamer character starts a 'game guild' within the Highschool DxD world. He recruits other characters from the series who have an interest in this new way of approaching the challenges in their world. Together, they embark on quests and missions, facing both in - school rivalries and otherworldly threats while using game - inspired teamwork and strategies.
A fanfiction could focus on a shy devil girl who has a secret crush on Issei. She tries to overcome her shyness and the social hierarchy within the devil community to confess her love to him. This could involve her learning about human emotions and relationships in the process.
One idea could be a female OC who is a transfer student with a unique Sacred Gear that no one has seen before. This could lead to all kinds of adventures as the characters in the Highschool DxD world try to figure out what it is and how powerful it could be.
One idea could be that the loli OC is a new transfer student at Kuoh Academy. She has a special power that she's unaware of at first, like the ability to communicate with mythical creatures. As the story progresses, she gets involved with the main characters from 'Highschool DxD' and they help her discover and control her power.
A really interesting plot could be Gasper getting transported to a different dimension or a parallel world within the DxD universe. In this new place, he has to rely on his wits and the basic powers he already has to survive and find a way back home. Along the way, he meets different versions of the characters he knows, and through his interactions, he learns more about himself and his place in the grand scheme of the DxD world.
One idea could be a crossover where Naruto's skills in combat and his never - give - up attitude influence the events in the Highschool DxD world. For example, he could help Issei train in a new and unique way, combining ninja techniques with the Boosted Gear. Another plot could involve Kuroka getting involved in a conflict that requires Naruto's special abilities to solve, like a mystery related to ancient ninja scrolls that have somehow ended up in the DxD universe.