In Death Note, the concept of justice is portrayed as a subjective idea through the perspectives of the main characters, Light Yagami and L. Light believes that justice is served by using the Death Note to eliminate criminals and create a utopian society, while L, the detective trying to catch him, believes in traditional methods of justice and the rule of law. This clash of ideologies highlights how each character's personal beliefs and values influence their definition of justice, ultimately showing that what is considered just or right can vary greatly from person to person.