There's a fanfic called 'Rias and Issei: A New Adventure'. In this one, they go on a journey together that tests their relationship. The author does a wonderful job of portraying their feelings for each other and the challenges they face as a couple in the world of Highschool DxD.
A popular fanfiction is 'Issei and Rias: United Front'. It portrays them as a powerful duo against their enemies. The author does an amazing job of writing their interactions, making it seem very natural. The story also has some great plot twists that keep readers engaged. You can find these fanfictions on various fanfiction websites. Just search for 'Highschool DxD Issei x Rias fanfiction' and you'll get a whole list to choose from.
One characteristic is the deepening of their emotional bond. These fanfictions often show their love story in different ways. Some might start from a friendship that slowly turns into a romantic relationship. Others may jump right into a more intense romantic scenario. Also, the fanfictions usually incorporate elements from the Highschool DxD universe, like the different factions and the power struggles, but with a focus on Issei and Rias's relationship within that context.
One great fanfiction idea could be that Issei discovers a new power within himself that is directly linked to Rias's heritage. Maybe he can tap into an ancient magic that only works in harmony with Rias's own powers. As they train together to master this new ability, their relationship deepens beyond just the typical master - servant bond in the Highschool DxD world.
Another common theme is the exploration of the different arcs from the series but with a focus on Issei and Rias. This could include their adventures in the Underworld, dealing with rival devil groups, or facing new threats together. Fanfictions may expand on these storylines while highlighting their relationship.
You can try fanfiction.net. It has a large collection of 'Highschool DxD' fanfics, including those centered around Issei and Rias. Just use the search bar and type in relevant keywords.
Many fans are drawn to the idea of seeing their favorite characters in romantic or more in - depth relationships. Issei is a relatable protagonist, and Rias is a strong and alluring character. Their combination in fanfics gives fans a chance to see more of their interactions, whether it's cute and fluffy or intense and passionate, that might not be fully explored in the original anime or manga.
The main reason is the chemistry between Rias and Issei in the original series. Fans love to explore their relationship further in fanfics. It gives them a chance to see different scenarios and what - ifs.
One possible fanfiction could involve a grand wedding ceremony. Issei, being the determined and passionate character he is, would make sure every detail is perfect for Rias. They might have a wedding that combines the elements of the devil world and the human world they both cherish. Friends from both sides would come together to celebrate their union. The story could also include some humorous moments, like Issei trying to learn the complex devil wedding traditions and getting things a bit wrong at first.
Power - up themes are also quite common. Issei often gets new powers or abilities, and Rias may play a role in that. For example, in some fanfictions, Rias helps Issei to master a new form of his Sacred Gear. This not only strengthens Issei but also deepens their bond as they train together. Another aspect is the exploration of the supernatural world in the context of their relationship. Since Highschool DxD has a rich supernatural setting, fanfictions may expand on this, like how Issei and Rias face new threats from the underworld or other dimensions together, which further cements their relationship and showcases their individual growth.