In 'Hellboy: The Crooked Man', Hellboy is the main focus, of course. He is a demon - like being raised by humans. He has a complex personality, being both tough and with a sense of humor, and he is constantly facing the dark forces that are part of his world.
Another one is 'Hellboy: The Crooked Man'. It features the iconic Hellboy character. Guillermo del Toro's touch can be seen in the way the story unfolds, with a blend of horror and mystery elements. The graphic novel is filled with his signature dark and grotesque visuals, which fans of his work really love.
Fanfics basically involve fans creating their own narratives based on the elements of something they love. It can be anything from imagining new adventures for characters to exploring alternate storylines. They're a way for fans to express their creativity and passion for the source material.
It's hard to say they are widely popular. They are likely only popular within very specific, niche communities that are interested in the particular theme related to a cockring. Most mainstream audiences would not be into this type of fanfic.
First, you need a clear idea or concept for your fanfic. Then, decide on the characters and their development. Start writing with an engaging beginning and build a compelling plot.