In the fanfiction world, Daryl kidnapping Rick could be a way to show his extreme possessiveness in the name of love. He might feel that Rick is always in danger when he's out in the open with the group. By kidnapping him, he's trying to create a private world for just the two of them. However, Rick is a strong - willed character, so he would fight against this confinement, but also start to question his own feelings towards Daryl during this struggle.
I'm not sure there are a lot of positive 'romance' scenarios where one character kidnaps the other in this context. However, in fanfiction, it could be a really twisted take on their relationship. Maybe the writer is exploring a darker side of Daryl's character where he feels compelled to kidnap Rick for some reason like he thinks it's the only way to protect him from a greater danger that Rick doesn't see. But this is quite a departure from their typical relationship in the show.
One great 'twd daryl and carol fanfiction' is 'The Journey Together'. It really delves into their relationship and the challenges they face in the post - apocalyptic world. The way it describes their unspoken bond is really captivating.