The fanfiction could center around the cultural differences between Issei and Serafall. Since they come from different backgrounds in the supernatural realm, there could be humorous and touching moments as they try to blend their cultures, for example, in their wedding preparations. Serafall might introduce Issei to her unique magical traditions, and Issei could share his human - like values with her.
Issei would likely become more confident and responsible. Marrying Serafall, a powerful figure, would force him to step up. He might learn new magical abilities or gain more respect in the supernatural hierarchy. For Serafall, she could become more in - touch with the human side of things through Issei. She may soften her more flamboyant and sometimes self - centered ways.
I haven't actually read a specific fanfiction with this plot. However, if such a fanfiction exists, it would likely involve a lot of creativity in terms of how the relationship between Issei and Serafall developed to that point. It could explore different aspects of their personalities and how they would handle the situation of a pregnancy, which might be quite different from the original storylines of their respective characters.
You can try fanfiction.net. It has a large collection of fan - created stories for various anime and manga, including High School DxD which Issei and Serafall are from. Just use the search function and type in 'issei x serafall' to find relevant fanfictions.
One popular one might be those that explore their unique relationship dynamic in the context of the High School DxD universe. For example, some fanfictions focus on how Issei's pervy nature interacts with Serafall's more flamboyant and powerful self. It could lead to some really interesting and comical situations, like when Issei accidentally makes a fool of himself in front of Serafall and she teases him mercilessly.
One possibility is that there would be a great deal of conflict within the story's world. Other characters might be shocked and try to interfere. For example, some might think it goes against the natural order or the rules of their society.
A fanfiction about Issei marrying Rias could explore the cultural differences within their world. Since Issei is human - turned - supernatural, and Rias is from a noble devil family. Their marriage could be a blend of human and devil traditions. They might incorporate elements like a human - style wedding reception with food and music, along with devilish ceremonies that are unique to Rias' family heritage. This would make their marriage a truly special and one - of - a - kind event in the fanfiction world.
There might be a fanfiction where Issei accidentally stumbles into one of Serafall's secret training grounds. Serafall is initially angry but then realizes Issei's potential. She decides to train him in some unique devil magic. This leads to a series of comical and at the same time, character - building events as Issei tries to master the new skills while dealing with Serafall's unpredictable nature.
They could have a very unique honeymoon. Maybe they would travel to different realms within their supernatural world. Issei would be excited to explore new places with Rias by his side. It could be a time for them to strengthen their bond further away from all the chaos and politics of their normal lives.
Well, the plot could involve Issei having to overcome many challenges to prove himself worthy of Sona. Maybe he has to battle powerful demons who oppose their union. He might also need to gain the approval of Sona's family or her peerage. It could also include some sweet moments of them getting to know each other better on a more personal level, like sharing their dreams and fears.