Yes, there might be. There are a vast number of fanfictions out there for various combinations of popular culture elements. Since Highschool DxD has a large fan base and Godzilla is an iconic figure, it's not unlikely that some creative fans have combined the two in a fanfiction. You can try searching on popular fanfiction websites to find such works.
There could be. Fanfiction writers are known for their wild and creative crossovers. Given the popularity of Highschool DxD and the unique concept of Guyver, it's entirely possible that an Issei - Guyver fanfiction exists. You might want to check popular fanfiction websites like Archive of Our Own or FanFiction.net. Just search for relevant keywords like 'Highschool DxD Issei Guyver' and see if any relevant stories pop up.
Yes, there are likely fanfictions out there with such a concept. In the 'Highschool DxD' universe, there are so many creative interpretations by fans. Some fanfiction writers might explore the idea of Issei taking on a Satan - like role for various reasons, perhaps to add a new twist to the story, explore different power dynamics, or to create unique character relationships.
One great Issei and Koneko fanfiction is 'The Bond of Opposites'. It delves into their relationship in a really interesting way. It shows how Issei's brash nature and Koneko's quiet demeanor play off each other.
In a fanfiction, it could be that Koneko and Issei are chosen for a special mission by the Gremory group. They are initially hesitant to work together as they have different approaches. However, as the mission progresses, they start to complement each other's styles. Koneko's stealth and Issei's more upfront fighting style work in harmony to defeat the enemy and complete the mission, and in the process, their relationship grows.
One great Issei and Ophis fanfiction could be where they team up to face a new powerful enemy. In this type of story, their unique abilities combine in interesting ways. For example, Issei's boosted gear and Ophis's dragon powers could create some really cool fight scenes. It might also explore their relationship further, perhaps showing how they grow to trust each other more on a deeper level.
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.
One great fanfiction idea could be Issei and Irina going on a special adventure together in the world of Highschool DxD. Maybe they discover a hidden power or a new realm. They could face challenges that test their relationship and grow stronger as a result.
One great fanfiction could be where Murayama discovers Issei's true nature as a devil early on. This could lead to some really interesting adventures as she tries to come to terms with it. Maybe she starts to train with him to be able to protect herself in the dangerous world of devils and fallen angels.
In a fanfiction, Issei and Koneko could be paired for a school project. At first, they struggle to work together because of their different personalities. Issei is more outgoing and impulsive, while Koneko is quiet and reserved. But as they dig deeper into the project, they start to understand each other better and develop feelings for one another.