Another popular OC is Mia. Mia is known for her intelligence. She's a strategist in the fanfics, and she helps Daryl and the group plan their defenses and raids. Her logical thinking and her ability to see things from different perspectives make her a great addition to the stories and a great match for Daryl.
Maybe the OC is a doctor who saves Daryl's life when he's severely injured. She then travels with him and the group, and their relationship develops as she tries to teach him some basic medical knowledge to help in future situations. They grow closer as he protects her from other hostile survivors.
No, Daryl Dixon is not a character in the comic version of The Walking Dead. He's an addition made for the TV adaptation to add more depth and diversity to the storylines.