“Don't be silly. I'm going to be with you all the way. No matter what…”
Sachiko is a woman of medium height with a slim build. She has straight, chin-length brown hair with bangs and small brown eyes. As a housewife, she dresses neatly but casually.
Sachiko is a kind and caring woman who deeply loves her family. She worries about her husband Soichiro's well-being while he works on the Kira case. When Soichiro is hospitalized due to a stress-related heart attack, she is frequently by his side to care for him. As concerned as she is about Soichiro, she also understands his convictions in working on the Kira case, and she stays by his side. Sachiko is proud of the academic success of her son, Light, and congratulates him on his good grades. When her daughter Sayu is wheelchair-ridden due to emotional trauma caused by her kidnapping, Sachiko aides her recovery, encouraging her and taking her for walks outside.
Sachiko is first seen waiting for Light to show her his exam grades. She is often at home when Light returns from school and is seen when the family eats or relaxes together. After the timeskip, she denies support for a match between her daughter Sayu and Touta Matsuda.
Sachiko Yagami is apparently never told that her son Light is Kira. It is likely that she is told he died in the battle against Kira like his father Soichiro. Near makes sure that the truth of Kira's defeat is never publicized, and in the manga, people simply believe Kira is resting.
Obata said that he had no real concept behind the design of Sachiko; he claimed that he encountered difficulty in drawing female characters who were not the main characters. Ohba did not include Sachiko in the final chapter of the manga but stated that someone in the Task Force would likely tell her that Light and Soichiro died in order to stop Kira, as the Task Force members would never let the world know the truth about the Death Note and the Kira case.