Overcoming obstacles is a big one too. There could be external forces, such as villains or difficult situations, that they have to face together. This tests their relationship and shows how far they are willing to go for each other, as seen in 'A Test of Love: Issei and Yumaa'.
Love and friendship are common themes. Their relationship often starts as a friendship that gradually evolves into something more. For example, in many fanfics, they support each other through tough times, which deepens their bond.
Adventure is also a theme. They might go on quests together, like in 'Issei and Yumaa: The Quest for the Lost Relic'. During these adventures, they discover more about themselves and each other, and it helps to strengthen their relationship.
There's also 'Issei and Yumaa: The Adventure Begins'. In this fanfic, they start on an exciting journey filled with magic and mystery. It's a relatively short but sweet story that focuses on their initial connection and how they start to rely on each other.
Love against all odds is also a frequent theme. Given their different positions and the nature of the High School DxD world, their love might be seen as something that goes against the norm. So, many fanfics will center around how they fight for their love in the face of various obstacles, whether it's social hierarchies or threats from other characters. It makes for a very engaging read as the story unfolds.
Another common theme is adventure. They often embark on various quests or face challenges together in the fanfic. For example, they might be fighting against common enemies in the supernatural realm. This not only tests their abilities but also strengthens their bond.
One common theme is the exploration of their relationship dynamics. Given that Ophis is a very powerful being and Issei has his own growth journey in the series, fanfics often delve into how they interact and influence each other's development.
A common theme could be the development of their relationship. Since it's a fan - created pairing, many fanfics might focus on how they get to know each other better, overcome differences, and grow closer.
Love and acceptance is also a very common theme. Given their different natures, the fanfics often explore how they come to love and accept each other for who they are. This can involve Issei accepting Ophis' more otherworldly aspects and Ophis learning to value Issei's human qualities like his compassion and determination.
One common theme is redemption. Often, the fallen angel character is seeking redemption, and Issei may play a part in that process. Another theme is the power of love that can overcome differences, as they are from different species in the story's context.
In many Issei x Irina Shodou fanfics, the theme of self - discovery could be present. Both characters might learn more about themselves as they interact with each other. For instance, they could discover new aspects of their personalities, powers (if applicable in their original context), or their life goals. This self - discovery often intertwines with their relationship, making it more complex and interesting.
Love and friendship are often explored as well. It could start as a friendship that gradually develops into something more. Or perhaps they are forced to work together due to some external threat and in the process, they develop deep feelings for each other. The stories might also touch on themes of loyalty and sacrifice as their relationship progresses.
One common theme is the exploration of their relationship. Since they come from different backgrounds in the anime universe, fanfictions often delve into how they get to know each other better and form a connection.