One common theme is love and its endurance. Since the series likely has elements of relationships, fanfictions may explore different aspects of love, like how it survives through difficult times.
I'm not sure specifically as I haven't fully studied this drama. But typically, there would be a male and a female lead who are central to the love story.
I haven't heard of a 'until we meet again soap' before. Maybe it's a new or independent production. If it's a story about a soap in a more metaphorical sense, like a story that revolves around a bar of soap and the memories or events associated with it until a future meeting, that would be quite an interesting and unique concept, but without more information, it's hard to say what the full story is.
I'm not sure as I haven't read this novel specifically. But usually, in a series novel, there are protagonists who drive the story forward. It could be a young couple, perhaps, given the somewhat romantic - sounding title.
I'm not sure as I haven't read it. But it could be about love or fate considering the title. The'red thread' often symbolizes a connection, and'meet again' might imply a story of relationships that are meant to be.
I'm not sure which specific 'until we meet again the series fanfiction' are the best. However, you could try joining fan groups or forums dedicated to the series. Fans there might be able to recommend some great fanfictions that they have read and loved. They can also give you insights into the different styles and plotlines of the fanfictions available.
Some local Asian bookstores, especially those that focus on Southeast Asian literature, might carry this Thai novel. You could also check with stores in your area that have a section dedicated to foreign language books.
Maybe an Imperial officer who is extremely cunning and ruthless. He might be obsessed with hunting down the Rebels and has a personal vendetta against them. He could use underhanded tactics and his knowledge of the Empire's resources to cause trouble for our heroes.
Maybe it has a young protagonist who is on a journey to find someone. And there could be an older, wiser character who guides the protagonist along the way. The red threads might connect the protagonist to the person they are meant to meet again, and these two main characters would play important roles in the story.