One important character introduced could be some of the new leaders of the local factions in the New World. They play a role in the political and military aspects that Ainz and his forces interact with. For example, there might be a new king or a powerful general.
In Overlord Vol 6, perhaps some new members of the various races in the New World are introduced. They might be important in terms of showing the diversity of the world. For instance, a new elven character with special magical abilities or a dwarven craftsman with extraordinary skills. These characters can influence the story through their interactions with the Nazarick inhabitants.
There could be new adventurers introduced. These adventurers might have unique skills and personalities. They could either become allies or enemies of Ainz and his group. Their presence adds more depth to the world as they have different goals and moral compasses compared to the Nazarick characters.
Ainz Ooal Gown remains the most important character. His decisions and actions drive the plot forward. He is constantly strategizing about how to expand his influence in the new world.
I'm not entirely sure about brand - new characters specifically in Vol 8, but existing important characters like Ainz Ooal Gown continue to be central. His actions and decisions drive the plot forward.
Albedo is another crucial character. She is extremely loyal to Ainz and her actions often support his plans. Her fanatical loyalty also adds an interesting dynamic to the story.
In Overlord Vol 4, Ainz is the central figure. He is the one who has to face all the challenges and make important decisions for his territory. Albedo is crucial as she not only aids Ainz but also has her own ideas and influence within Nazarick. Additionally, Demiurge, with his devious and intelligent mind, plays an important part in the story, often coming up with strategies and plans for Ainz's rule.
Ainz Ooal Gown is of course one of the most important characters. He is the master of Nazarick and drives most of the events in the story. Albedo, his loyal and somewhat possessive subordinate, also plays a significant role. She is often involved in the decision - making processes within Nazarick. Then there are the other floor guardians like Shalltear Bloodfallen who are important in battles and maintaining the order of Nazarick.
I'm not entirely sure without reading it, but it's possible that no new major characters are introduced and the focus remains on Kazuma, Aqua, Megumin and Darkness.
One important new character is from a previously unintroduced race. This character has a special connection to the magic of the New World and their appearance shakes up the existing power structure. They interact with Ainz's forces in unexpected ways, leading to some tense and interesting situations. Another new character is a young prodigy in a certain type of magic who catches the attention of Ainz's subordinates and may play a role in future developments.
The important new character in Durarara Vol 5 Light Novel is Aoba Kuronuma. He's a complex addition to the cast. Aoba has an air of mystery around him. He quickly becomes enmeshed in the power struggles and the web of relationships in Ikebukuro. He seems to have his own agenda, which isn't fully clear at first. As the story progresses, we see how his actions and his personality start to shape the events. He also has an impact on the way the other characters view their own situations and the state of the city as a whole. His presence really shakes things up in the already chaotic world of Durarara.
One important character introduced could be new allies that Rimuru meets. They might have special abilities or knowledge that help Rimuru in his adventures. For example, there could be a powerful mage or a skilled warrior.
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.