One popular character is Frances Neagley. She often plays an important role in fanfiction as she has a strong connection with Reacher. Another could be Finlay, who has his own charm and can bring interesting dynamics to the fan - created stories.
There is often a local police officer who teams up with Reacher. This officer usually provides the local knowledge and access to official resources that Reacher needs. They work together to solve the crimes in the area.
One common theme could be loyalty. Given the nature of Daryl Dixon's character in the original show, loyalty to friends or comrades like Gene Dixon and within the context of Trinity might be a big part of the fan fictions.
Reacher is purely fictional. The characters and events are made up to engage the audience and provide an exciting narrative. It doesn't draw from real-life events or people.
Daryl Dixon isn't gay in the comics. The storylines mainly revolve around his adventures and struggles in a post-apocalyptic world, not his sexual orientation.
It depends on their popularity and the creativity of fans. If people are really into their characters and potential relationship, fanfiction could definitely exist.