The main character is surely important. His actions and decisions drive the story. There may also be his loyal followers within his shadow organization. And characters who are unknowingly being influenced by his behind - the - scenes machinations.
I'm not sure who exactly is newly introduced in this volume. But in the series, the main character is Cid Kagenou. He's the one driving most of the plot with his shadow - related activities.
I haven't read this volume specifically, but generally in the series, there are often plot points related to the protagonist's secret identity and his actions behind the scenes. It might involve new challenges he faces in the shadow world or developments in his relationships with other characters.
In this volume, we might see the continued growth of the main character's shadowy influence. There could be new challenges for his secret organization and how he manipulates events from the shadows to achieve his goals. Maybe new characters are introduced who either become part of his schemes or pose a threat to his hidden plans.
New characters in Eminence in Shadow Vol 5 could be ones that are connected to the deeper mysteries of the world. Maybe they are part of a secret organization that the main character stumbles upon. They might have their own motives and goals that at first seem at odds with the main character's, but as the story progresses, there could be some sort of alliance or conflict that arises from their interactions. Their introduction might also serve to expand the lore of the series by bringing in new elements related to the world's history or magic.
Well, in Eminence in Shadow Vol 5, there could be developments in the relationships between the characters. Maybe the main character gets closer to some allies while deceiving his foes even more effectively. There might also be new revelations about the world's magic system or power structure that he has to navigate through.
The Eminence in Shadow light novel is finished. It provided a conclusive ending for the characters and their adventures, leaving fans with a complete narrative.