One great 'tails and marine' fanfiction could be 'The Adventures of Tails in the Marine World'. It has an interesting plot where Tails discovers a hidden underwater civilization. He uses his mechanical skills to help the marine creatures there, which makes for an exciting read.
Adventure is also prevalent. They often go on exciting journeys together, like exploring new islands or searching for lost treasures. These adventures allow for character growth and development.
Another option is to check out some niche fanfiction communities on social media platforms. For example, there might be groups on Reddit dedicated to this kind of fanfiction. You can ask the members there if they know of any good 'tails and marine' stories or where to find them.
One common theme is friendship. Since Tails and Marine are from different worlds, their growing friendship is often explored. Another theme is adventure. They usually embark on some sort of journey together.
One common theme is the 'forbidden love' aspect. Since Tails is from the land and Marine is from the sea, their different habitats can be seen as a barrier, like in Romeo and Juliet. Another theme is discovery. They discover new things about each other's worlds and themselves through their relationship.
First, you need to create your characters. Decide on the species they are, their personalities, and their special abilities. For example, if one is a mermaid with a tail, what color is the tail and what can it do? Then, think about the setting. Is it a deep - sea trench or a coral reef area? After that, come up with a basic plot, like they are searching for a lost treasure.
One popular marine and tails fanfiction is 'The Adventure Beyond the Waves'. It takes the characters on a journey across uncharted seas, facing various challenges and making new friends along the way. The story beautifully captures the essence of their personalities.
I'm not sure if it's still available, but 'The Tale of Tails and Marine' was quite a hit. It was a bit different as it incorporated elements of time - travel. Tails somehow travels back in time and meets a younger Marine, and their relationship develops in a very unique and unexpected way.
Adventure is also a popular theme. Since both characters are associated with exploration in their own ways, fanfics often have them going on exciting adventures together, like finding hidden treasures or exploring uncharted lands.
Some tails and marine related fanfiction could focus on their adventures in an underwater world. For example, they could be on a quest to save their ocean home from pollution. They might team up with other sea creatures and use their unique abilities, like tails being able to control water currents, to overcome obstacles.