Common themes include the struggle between good and evil. The fallen angel has a complex relationship with the concepts of good and evil, and Issei's interaction with them adds another layer to this. There's also the theme of acceptance. They have to accept each other's flaws and differences. This is often portrayed through their emotional and physical interactions, and how they grow as characters through these experiences.
A frequently seen theme is the exploration of identity. The fallen angel may be struggling with their identity as a fallen being, and Issei's presence can either reinforce or change that perception. Also, the theme of loyalty comes up, as they face various challenges that test their loyalty to each other. The relationship between them also often challenges the existing power structures in the fictional world they inhabit.
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.
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.
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.
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.
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.
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.
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.
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.
One common theme is redemption. Often, the fallen are portrayed as having a chance to be redeemed through their interactions with the guardians. Another theme is cooperation, as they have to work together despite their differences. And of course, there's the theme of discovery, both in terms of learning about each other's cultures and abilities.
One popular issei x fallen fanfic is 'A New Bond'. It explores the relationship between Issei and a fallen angel in a unique way, with interesting character development and a plot full of twists. Another one could be 'Fallen's Redemption' which delves into how the relationship changes the destinies of both characters.
Alliance is also a theme. The idea of a Guardian and a Fallen teaming up against a greater threat, perhaps something that endangers both of their species. This can lead to some exciting adventure - type stories.