It's possible that there will be new characters from other regions. For example, a warrior from a far - off land who has heard of the Goblin Slayer's deeds and comes to offer assistance or seek training. Or perhaps a healer who specializes in treating the wounds caused by goblins. There might also be a character who has some sort of connection to the origin of the goblins, like an ancient scholar or a hermit who holds the key to understanding the goblins' true nature.
Maybe some survivors of goblin attacks who decide to join the fight. They could have unique skills or knowledge about the goblins. Another possibility is some sort of magical being that has an interest in the goblin situation, either to help or hinder the Goblin Slayer.
Maybe some new demon slayers from different regions. They could have unique fighting styles.
Not having read Volume 9, we can only speculate. It's possible that there are new characters who are part of an order or organization that has a different view on dealing with goblins. There could be a new female character who is a skilled archer and has her own reasons for hunting goblins. Or perhaps a mysterious figure who seems to know more about the origin of the goblins than anyone else and their presence shakes up the status quo among the adventurers and the Goblin Slayer.
There could be new support characters such as a healer or a mage with unique abilities. These new characters might bring new perspectives to the story. They could also have different relationships with the existing characters like the Goblin Slayer. For example, a new character might be initially skeptical of the Goblin Slayer's extreme methods but later come to understand them.
We might expect more intense battles against goblins. Maybe new strategies and weapons will be introduced by the Goblin Slayer.
The main character is the Goblin Slayer himself. He's the one focused on killing goblins.
There could be new pilots. Maybe some younger recruits who bring a fresh perspective to the team.
Goblin Slayer is of course a very important character. He is the main protagonist focused on slaying goblins. Priestess is another important one. She often accompanies Goblin Slayer on his missions and uses her healing and support magic. High Elf Archer is also significant. She provides ranged combat support in battles against goblins. Dwarf Shaman helps with his knowledge of magic related to earth and such elements which are useful in combat situations against goblins.
I'm not sure specifically as the 'vampire slayer new blood story' isn't a widely known established story that I have all the details on. But it could have the new vampire slayer as a main character, of course. There might also be a vampire antagonist who is particularly powerful or cunning.
There could be a young elf named Twinkle who is new to Santa's workshop and is trying to prove himself. He might get into all sorts of comical mishaps while trying to make toys.
One possible character could be an angel. This angel might be sent to Earth to help a family in need during Christmas. Another could be a stray dog that finds a warm home during the holidays. And then there's the postman who delivers all the Christmas cards and gifts, and he might have his own little story within the new Christmas story.