I'm not sure as I haven't read it yet. But it could be characters who are known for their defiant nature, like rebels or non - conformists.
Since it's about life in defiance, the main characters might be those who are fighting against something. It could be a young person defying the old - fashioned rules of their family, or a group of people defying a corrupt system. Without reading the book, it's hard to say exactly who they are, but they are likely to be individuals with strong wills.
There's no way to know for certain without reading the novel. However, we can assume that the main characters are ones that the author wants to showcase as being in a state of defiance. They could be from different backgrounds, perhaps some are marginalized individuals who have decided to take a stand. Maybe there's a lead character who is on a journey of self - discovery while also defying the odds stacked against them.