Well, I know a fanfic where Issei and Gabriel team up against a common enemy. In this story, their relationship blossoms as they face challenges together. It's really interesting to see how their different personalities complement each other in the story.
The contrast between Issei's more earthly and often brash nature and Gabriel's celestial elegance. It creates a dynamic that can lead to really interesting character interactions in the fanfic.
You can try fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Highschool DxD Issei x Gabriel' on their search bars, and you should be able to find relevant fanfictions.
The fanfictions also allow for a deeper exploration of the characters' personalities. Issei's determination and Gabriel's grace can be further developed. Writers might give them new backstories or put them in situations that are not in the original anime. This gives readers a fresh perspective on the characters and their relationship, which is what makes these fanfictions so interesting.
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.
I really like the fanfic 'Koneko's Heart for Issei'. In this one, it delves deep into Koneko's emotions towards Issei. It starts with her being a bit reserved but as the story progresses, her true feelings start to surface. Another interesting fanfic is 'Issei and Koneko: United'. This fanfic shows how they work together to face challenges in the Highschool DxD world, and their relationship blossoms as they rely on each other.
One great fanfic could be 'Issei and Gasper's Unlikely Bond'. It delves into how their friendship develops in a unique way, with some exciting adventures in the Highschool DxD universe. They face challenges together and support each other, which is really heart - warming.
Well - developed characters make it interesting. If the original character (OC) has a unique personality, backstory, and goals, and their relationship with Gabriel is complex and evolving, it can be really engaging. For example, if the OC is a half - demon who struggles with their identity and Gabriel helps them come to terms with it.
Maybe there's a prophecy in the Highschool DxD universe that involves Issei and Mirana. They are brought together by fate, but they don't know it at first. Issei is on his usual adventures, fighting devils and whatnot, and Mirana gets caught up in his world. Their relationship starts to form as they work together to figure out the prophecy and in the process, they fall in love. There could be a lot of action, drama, and some romantic moments along the way.
One great Issei x Katase fanfiction is 'A Different Path'. It shows an interesting alternate universe where their relationship develops in a unique way. It focuses on their interactions and how they support each other through different challenges in the Highschool DxD world.