I'm not entirely sure about brand new characters introduced only in Volume 7. But of course, Bell Cranel remains very important. His growth and development are central to the story. And Hestia, as his goddess, is always significant. Other existing characters like Ais Wallenstein also continue to have an impact on the events in this volume through their interactions with Bell.
Well, Bell Cranel is without a doubt one of the most important characters in Volume 7. He's the protagonist, and his actions drive the plot forward. Hestia, his goddess, is always there to support him in different ways. Ais Wallenstein, the beautiful and powerful swordswoman, also has her part to play. While I can't recall any truly brand - new characters that stand out immediately, the way these established characters interact and develop their relationships within the context of this volume is really what makes it interesting.
I'm not entirely sure about all the new characters in volume 14. But sometimes new characters are introduced to either help or hinder the main characters' progress. They could be other adventurers, or perhaps some mysterious figures related to the dungeon's secrets.
There might be new adventurers who join Bell's party temporarily or become their rivals. These new characters could bring in new skills and perspectives. Maybe there are also some characters from the background of the dungeon world, like merchants or informants who have important information related to the new challenges in Volume 8.
Unfortunately, without having read Danmachi Volume 19 Light Novel in full, it's difficult to name the new characters precisely. But typically, new characters in the series are designed to bring fresh challenges and interactions. They could be powerful adventurers that Bell and his friends have to team up with or compete against, or they could be some strange creatures from the deeper parts of the dungeon with their own motives and behaviors.
Bell Cranel is surely one of the important characters as he is the main protagonist. His actions and growth are central to the story.
One important character could be new adversaries that Ainz and his group face. These characters bring new challenges and often have unique abilities or motives. Another might be some minor characters within the native population of the new world that help to flesh out the world - building aspect.
In this volume, the Lizardmen leaders such as Crusch Lulu are important. They represent the native species that Ainz has to deal with. Among Ainz's subordinates, Demiurge also stands out. He is very intelligent and his strategies and ideas are important for Ainz's plans. There are also other minor characters among the lizardmen tribes that add to the richness of the story.
I'm not entirely sure which new characters are introduced specifically in volume 9. But generally, in the Overlord series, characters like Ainz Ooal Gown remain extremely important. His actions and decisions drive most of the story. The floor guardians such as Albedo also continue to be significant as they carry out Ainz's orders and protect Nazarick. There may be some minor characters from the human kingdoms or other races that are introduced to show the different perspectives in the world.
Based on the general trend of the Shield Hero light novels, volume 7 may introduce characters who are related to the ongoing story arcs. Since Naofumi is constantly facing new challenges, new characters could be those who hold keys to solving problems or creating new ones. For example, there could be new magic users who have different views on Naofumi's power. Raphtalia and Filo will remain important as they are part of Naofumi's core group. And there could be some authority figures in the world who start to take notice of Naofumi's actions in this volume and interact with him, thus becoming important characters in this part of the story.
It's possible that in volume 6, some characters from different classes who were previously in the background come to the forefront. These characters might have unique skills or knowledge that can either help or hinder the main characters. Also, there could be some characters related to the school's management system, like those in charge of specific tests or evaluations, who are introduced to add more complexity to the story and the relationships among the students.
I'm not entirely sure which new characters are introduced specifically in volume 4. But it's likely that there are characters related to the new races or groups that the siblings encounter. Maybe there are some game masters or representatives of different factions.