The main character is surely the guard. There could be a villain or a group of antagonists that he has to face. Maybe there's also a mentor figure for the guard, someone who has taught him the skills he needs for his job and offers him advice throughout the story.
One of the main characters is Andy. She's an ancient warrior and a leader among the immortals. Another is Nile, a new addition to the group who brings a fresh perspective. Booker is also important; he has his own set of issues and a long history.
In the 'Mouse Guard Graphic Novel', the main characters are a group of mice that form the Mouse Guard. Saxon is a strong and fearless mouse. Kenzie is the brains behind many of their plans. Lieam is young but very capable. There are also other mice that they interact with in their community, like the elders who give them advice and the common mice they are sworn to protect. Each character has their own backstory and development throughout the stories in the graphic novel.
One of the main characters is Andy. She is a very old and experienced immortal.
I don't know for sure as I haven't read the novel. But they could be people who have lived near the Nile for generations and have some important role to play in the story.
Mortarion is also a central character. His journey from a Primarch to a servant of Nurgle is a major part of the story. His decisions and actions shape the fate of the Death Guard as a whole.
In the 'Regal Guard of Dragon' novel, there could be a main character who is a dragon - tamer within the guard. This person would have a unique connection with the dragons and play a crucial role in the guard's operations. There may also be a character who is an outcast from another group but finds a new purpose and family within the regal guard. Another possible main character could be a wise elder who has a vast knowledge of the dragons and their history, guiding the younger guards.
I'm not aware of the exact main characters in 'the young imperial guard novel'. However, it's likely that among the main characters are some exceptional young guards who stand out. There could be a young guard with extraordinary combat skills or a very intelligent one who can solve complex problems within the imperial guard's scope of work. And perhaps there are also some important figures in the imperial court who interact with these young guards and play important roles in the story.
In 'princess guard visual novel', the princess is surely a main character. She could be a damsel in distress or a strong - willed leader in her own right. The guards are also main characters. They might come from different backgrounds, some could be noble - born, others might be self - made heroes. There could also be antagonists, like those who try to harm the princess or undermine the guards' efforts.
Since we don't have much information about 'the old guard story', it's difficult to determine the exact main characters. But they might be individuals who have been around for a long time within the context of the story. If it's a story about a small town, the main characters could be the long - time residents who have seen the town change over the years and are now considered the 'old guard'. They could be the ones who hold the key to the town's traditions and history.
I don't know for sure, but probably the main characters from the first 'The Old Guard' will return. Like Andy, who is a key figure among the immortals.