One great Wing Diver x Wing Diver fanfic could be about their adventures together in a post - apocalyptic world. They might face new and dangerous monsters while relying on each other's skills.
You can start by looking on popular fanfic websites like Archive of Our Own. They have a wide range of fanfics from various fandoms, and there's a good chance you'll find some Wing Diver x Wing Diver ones there.
The diving part itself. Real divers go through similar procedures like checking equipment, descending into the water, and dealing with the underwater environment which are reflected in the game. Also, the types of sea creatures in the game are based on real ones that divers might encounter.
One key element could be the main character's journey. Another might be the presence of some kind of magical or special items. And there could be a struggle against an opposing force.
The 'Holy Diver' game story might involve a journey of a hero in a fantastical world. Maybe there are quests to complete, like rescuing a sacred artifact or saving a group of people from an evil force. However, without more specific information, it's hard to be more detailed.