In Death Note, the main character Light Yagami initially starts using the Death Note, a notebook that allows him to kill anyone by writing their name in it, with the intention of creating a world free of crime and becoming a god-like figure known as "Kira." He believes that he is bringing justice to the world by eliminating criminals and wrongdoers. However, as the series progresses, it becomes clear that Light's pursuit of justice is driven more by his desire for power, control, and personal gain rather than a genuine interest in bringing about a just society. This transformation highlights how the concept of justice can be twisted and manipulated for selfish reasons.