Voiced by: Haruka Kudō (Japanese), Kelly Metzger (English), and Kristie Marsden (English).
Sayu Yagami (夜神 粧裕, Yagami Sayu) is Light's younger sister. Like her mother she never learns of Light's possession of the Death Note or his identity as Kira. In the manga and anime, Mello's gang kidnaps her in exchange for the Death Note possessed by the investigation team. Although being returned unharmed, Sayu falls into a state of shock, eventually becoming unresponsive to the presence of others. In the live-action films her character is portrayed by actress Hikari Mitsushima, and since the mafia does not play a role, she is not kidnapped.
Though not having any real concept behind Sayu's design, artist Takeshi Obata states that he often encounters difficulty in drawing female characters not central to the storyline. Author Tsugumi Ohba considers Sayu and her mother as two of the purest characters in the series, stating that he could not "sense any evil or twistedness from these two at all." Both creators added that they considered the Yagami family to be the most pitiful characters in the book; Ohba later adding that he felt sympathy for Sayu and her mother.