In "Death Note," the theme of sacrificing morality for the greater good is primarily showcased through the main character, Light Yagami. Light initially believes that using the Death Note to rid the world of criminals is a necessary sacrifice of his own morality for the greater good of creating a perfect and just society. However, as the series progresses, Light's actions become increasingly ruthless and he begins to manipulate and harm innocent people in pursuit of his goal, blurring the lines between what is morally justifiable and what is not. Ultimately, the story challenges the notion of sacrificing morality for the greater good by portraying the consequences and ethical dilemmas that arise from such a choice.