Sayu Yagami

Sayu is cheerful, friendly and comparatively carefree during the opening portion of the story. She admires Light as a highly capable older brother and readily asks him for help with her schoolwork.

Unlike Light, she does not share her father's intense involvement with criminal investigation. She reacts to the Kira case primarily as an ordinary young person hearing about frightening events through television and her family.

Her personality changes significantly following traumatic events later in the story. After being kidnapped by Mello's organization and subsequently rescued, Sayu suffers severe psychological trauma and becomes withdrawn and largely unresponsive for a period.

Sayu has no supernatural powers and is never involved in using the Death Note. She is an ordinary student without established combat or investigative training.

Her complete lack of involvement with the notebook is important to her place within the Yagami family. She does not know Light's secret and has no meaningful way to protect herself when the Kira conflict eventually reaches her directly.

Sayu initially appears in domestic scenes with Light, Sachiko Yagami and Soichiro. She asks Light for help studying and helps establish his outward identity as an accomplished, dependable older brother.

Years later, the struggle over the Death Note expands beyond the original Japanese investigation. Mello, seeking a notebook for himself, targets the family of the NPA official responsible for it.

Mello's Mafia kidnaps Sayu and demands the Death Note held by the Japanese Task Force in exchange for her life. Soichiro travels to the United States and ultimately hands over the notebook to secure his daughter's release.

Sayu survives the kidnapping but is left deeply traumatized. Later appearances show signs of gradual recovery, including attending her coming-of-age ceremony.

Light Yagami is Sayu's older brother. She admires his intelligence and asks him for help with schoolwork, remaining unaware of his identity as Kira.

Soichiro Yagami is Sayu's father. He places her safety above retaining the Death Note and participates directly in the effort to secure her release after her kidnapping.

Sachiko Yagami is Sayu's mother and shares the family's anxiety over the dangerous circumstances surrounding Soichiro's work.

Mello orders Sayu's kidnapping so that she can be exchanged for the Death Note held by the Japanese authorities.