Maybe Cosmo was turned into a different form, like a small, helpless creature. Tails stumbles upon her in this state while on a routine exploration. At first, he doesn't recognize her, but as he gets closer, he realizes it's Cosmo. He then devotes all his time to finding a way to turn her back to her normal self. Along the way, they form a deeper bond, and when she finally returns to her original form, it's a beautiful reunion.
Once upon a time, in a far - off land filled with strange and wonderful creatures, Tails was on a journey. He had been searching for Cosmo for what seemed like an eternity. One day, as he was exploring a mysterious forest, he heard a faint rustling. Turning around, he saw a figure that made his heart skip a beat. It was Cosmo. She had been lost in a different dimension, but through some strange magic, she had found her way back. Tails ran to her, his tails spinning with joy, and they embraced, tears in their eyes, knowing they would never be parted again.
They would become more protective of each other. Tails would be constantly looking out for Cosmo during her pregnancy, making sure she's comfortable and has everything she needs. Cosmo would also be more dependent on Tails, and their bond would strengthen as they are about to become parents.
One common theme is sacrifice. Since Cosmo has a selfless nature in the original story, fanfictions often explore her willingness to sacrifice for the greater good or for Tails. Growth and self - discovery are also themes. Tails, being a young and intelligent character, often goes through experiences in fanfictions that help him understand himself and his place in the world better. This is sometimes related to his relationship with Cosmo, as she can be a catalyst for his growth.
One common theme is friendship. Tails and Cosmo are often depicted as having a very strong bond. Another theme is adventure, as they are usually involved in some exciting exploration or mission.
Another theme is growth. Both characters develop throughout the fanfictions. Tails might become more confident in his abilities outside of just technology, and Cosmo could learn more about the world around her and how to better control her powers. This growth is often a result of their experiences together and the challenges they face as a duo.
One possible idea in Cosmo and Tails vines fanfiction could be their adventure in a magical forest. Cosmo, with her plant - like abilities, might discover a new type of flower that has the power to heal any injury. Tails, being the smart inventor, would try to analyze the flower's properties. They could face challenges like protecting the flower from evil forces who want to use it for bad purposes. This would create an exciting story full of action and discovery.
I'm not sure about the common themes in this specific 'cosmo and tails collar fanfiction' as I haven't studied it in detail. But it could potentially involve themes of friendship, adventure, or unique relationships given the characters of Cosmo and Tails.
A simple fanfiction could be about Cosmo and Tails going on a picnic. Cosmo brings some special plants she grew herself for their meal, and Tails flies them to a beautiful meadow. It's a peaceful and cute story idea.