We can also look forward to more details about the world - building. The earlier volumes have given us a glimpse of the unique setting, and this volume might expand on it. For example, we could learn more about the social hierarchy or the cultural traditions in the story's world.
Well, perhaps more character development. In previous volumes, we saw the relationship between the main characters evolving, and in volume 5, it might continue that trend. There could be new challenges for the couple to overcome, which would further strengthen their bond.