Well, it could be an alien race that has control over the rift and doesn't want Owen to be rescued. They might see him as a threat or an interesting specimen to study.
One possible plot development could be that the team at Torchwood desperately tries to find a way to bring Owen back from wherever the rift has taken him. They might search through old Torchwood files and artifacts for any clues on how to reverse the rift's pull.
One common theme is survival. Given Owen's often - precarious situations in the show, many fanfictions explore how he manages to survive against all odds. For example, in some stories, he has to deal with life - threatening alien encounters alone.
I'm not entirely sure as I haven't read it specifically. But generally, in the Torchwood universe, it might deal with the rift and the strange phenomena and battles associated with it. It could involve the Torchwood team facing off against alien threats that come through the rift.
Another interesting one is 'Owen and the Unseen Threat'. In this fanfiction, Owen has to face a new, mysterious threat all by himself while the rest of the team is preoccupied. It shows his resourcefulness and determination, and the author does a great job of creating suspense throughout the story.
You can try looking for it in large bookstores. They usually have a section for graphic novels, and they might carry the 'Torchwood Rift War Graphic Novel'.
In such a fanfiction scenario, first of all, the Volturi would likely have their reasons for taking Renesmee, perhaps believing she is a threat to the vampire world order. Once taken, the Cullens would be desperate. Alice might use her visions to try to find Renesmee's location. Jacob could also play a crucial role as he has a special bond with Renesmee. He may attempt to lead a rescue mission or at least try to communicate with her while she is in the Volturi's custody. The story would be filled with drama, action, and the exploration of relationships between different characters in the 'Twilight' universe.
In the 'ponyboy gets taken by a demon' fanfiction, a lot can unfold. First, the demon might have been observing ponyboy for a while, waiting for the right moment to strike. Once taken, ponyboy could be exposed to all kinds of strange and terrifying things in the demon's world. He might meet other captives or creatures there. He would have to rely on his wits and any latent courage he has. There could also be a chance that he discovers some sort of connection between himself and the demon's world that he never knew before, which could either help him escape or make his situation even more complicated.
In some fanfictions, it could be an unknown alien species. They might have detected Bumblebee's unique energy signature and decided to take him to study his technology or abilities. This could lead to all sorts of interesting adventures as Bumblebee tries to communicate with them and find a way to escape.
Another popular one is 'Slow Decay'. It explores the darker side of Torchwood and the moral dilemmas the team often faces. The complex characters and the engaging storyline make it a favorite among many Torchwood fans.