Keeper of the Gate of Grudges presents each soul with three choices: pass through the Gate of Grudges to heaven and be reborn, refuse to admit death and remain as a ghost on earth, or haunt and kill one person and then proceed to hell and eternal suffering. Izuko was a stillborn baby, so she arrived at the gate without even knowing which option she would choose. In the end, the superiors (not cleary if the superiors are demons, gods or etc) decided to mantain her as the gate keeper. The only rule is that she can't choose the option for the person, or she would fall in hell.
In the end of the manga, Izuko, whose real name is unknown, decides to take the path to be reborn and the gate keeper role is passed down to Anna. The previous gate keeper then goes to earth to see her little sister living happy. She says that she wants to meet her someday and, from the sky, she looks to the living world,while proceeding to a new life.