Since we don't know the exact plot of 'the wall graphic novel', it's difficult to determine the main characters. They might be a group of rebels who are fighting against the existence of the wall, or perhaps a family that has been split because of the wall. There could also be a character who has the power to change the fate of the wall, whether it's a political figure or someone with a special ability.
There's no way to know for sure without reading the graphic novel. However, it's possible that the main characters include a young person who is curious about what's on the other side of the wall. Maybe there's also an older character who has memories related to the origin of the wall and serves as a guide to the younger characters in understanding the wall's significance. And there could be a character who represents the authority that maintains the wall, adding conflict to the story.