In Death Note, the protagonist Light Yagami initially views his use of the Death Note, a supernatural notebook that allows him to kill anyone by writing their name in it, as a tool for creating a just and crime-free world. However, over time, Light's pursuit of justice becomes entangled with his personal desire for power and control. As Light continues to use the Death Note, his definition of justice becomes skewed, ultimately leading to his downfall. The series effectively explores how the concept of justice can be manipulated and used for personal gain, highlighting the moral complexities that arise when someone seeks to impose their own sense of justice on others.