In "Death Note," guilt plays a significant role in influencing the decisions of the characters, particularly Light Yagami. As Light takes on the role of Kira and starts using the Death Note to kill criminals, he initially justifies his actions as a way to create a better world by reducing crime. However, as the series progresses, Light starts to feel the weight of his actions and experiences guilt over the lives he has taken. This guilt ultimately impacts his behavior and decisions, leading to a transformation in his character as he grapples with the consequences of his choices.