Well, it could be a story where Riddick gets dropped into The Walking Dead world and meets Daryl. They might start off as distrustful of each other. Daryl, being cautious of strangers, would be wary of Riddick. But as they face more and more zombies together, they learn to respect each other's skills. Riddick could teach Daryl some new ways of combat, and Daryl could show Riddick how to better navigate the post - apocalyptic landscapes of The Walking Dead.
It could be an exciting crossover. Riddick is known for his survival skills in harsh environments, and Daryl from The Walking Dead is also a great survivor. In the fanfiction, they might team up to fight against the zombies in The Walking Dead universe. Maybe Riddick's unique fighting style and his ability to see in the dark would give them an edge in battles.
In this fanfiction, perhaps there could be a plot where a powerful group in The Walking Dead world tries to capture Riddick, thinking he could be a valuable asset or a threat. Daryl, having formed a bond with Riddick, decides to help him. They go on a journey to find a safe place away from this group. Along the way, they share stories of their pasts, with Riddick talking about his time in prison and Daryl about his family. This interaction would make for an interesting and engaging fanfiction.