Age: 12 years old
Hair: Black
Eyes: Black

Sakiko is Maruko-chan's older sister. Sakiko is a sixth grader who is clever, calm and organized, the exact opposite of her younger sister, Maruko. She and Maruko share a room and often fight but they get along. She attends the same school as Maruko. She is afraid of roaches and blame Maruko who always eat snacks in their bedroom.