The main character is likely the executioner herself. But there may also be other characters like her superiors, the people she is supposed to execute, or perhaps some friends or allies she might have.
In 'the executioner and her way of life light novel', the executioner is surely a main character. There could be characters who oppose her actions, like those who believe in mercy and forgiveness. There might also be side characters such as the guards or assistants who work with her. Additionally, there could be characters from her past that have influenced her way of life and her current role as an executioner.
The most prominent character is the executioner. However, we may also see characters who are part of the justice system in the novel's world. There could be a mentor - like figure who taught her the ways of being an executioner. And there may be characters who are victims of the system she is part of, which could lead to some interesting interactions and moral dilemmas for the executioner.