It depends. Some consider them canon if they fit seamlessly into the established Samurai Jack universe and don't contradict the main storylines. Others might have different opinions.
It depends. Different people and franchises might have different criteria for what constitutes canon. Sometimes it's clearly defined, other times it's more ambiguous.
Detective Conan Akai Shuichi:
In Detective Conan, Akai Shuichi was a mysterious detective whose identity had always been a mystery. He had worked with the organization before, but the identity and purpose of the organization had always been unknown. Akai Shuichi's character was very dangerous. His skills and skills were top-notch, and he was very persistent about his goal. In the story, Akai Shuichi appeared many times and fought fiercely with Conan and others. He was a very interesting character.
One characteristic is the exploration of their complex relationship. Akai and Conan are both intelligent characters, and fanfics often play with their dynamic, like who's leading in a case or who has more knowledge. Another is the mystery element. Since both are involved in detective - related scenarios, fanfics usually have a lot of mystery, with hidden clues and unexpected plot twists.
One common theme is mystery. Given his role in the source material, many fanfictions explore his past, his undercover operations, and the secrets he holds. For instance, some stories might dig deeper into how he became such a skilled detective.
The main characters are Akai and Akemi. Akai is often portrayed as a strong and brave character, while Akemi is usually depicted as kind - hearted and intelligent.