Sakiko Sakura is the 12-year-old elder sister of Maruko. Her black hair typically appears in two small pigtails secured by pink hairbands, featuring seven distinct bangs identical to Maruko's. She wears it shoulder-length during sleep or special occasions. Her standard outfit combines a red-pink long-sleeve blouse with a white collar, a blue-green knee-length pleated skirt, white socks, and yellow outdoor shoes.

Well-behaved, clever, calm, and organized, Sakiko contrasts sharply with Maruko's impulsiveness. She frequently advises Maruko but may sour into foul moods post-argument, despite rarely provoking conflicts. She harbors an ardent fan crush on singer Hideki Saijo, evidenced by his poster in their shared bedroom and her dedicated viewings of his TV appearances. Maruko's eccentric public behavior often sparks intense embarrassment in Sakiko, who habitually masks these reactions.

Sakiko pursues varied interests: reading about star signs, birds, and wildlife; playing the recorder; scooping goldfish (skillful enough to catch two simultaneously); and crafting through knitting, origami, and flower-bow tying. Her favored foods include eel, katsudon, ramen, and gratin. She receives a ¥3000 monthly allowance and treasures a necklace from a friend. Deeply afraid of cockroaches—often blaming Maruko’s room snacking for attracting them—she also fears snakes and frogs.

Sharing a room with Maruko triggers frequent lighthearted fights. Sakiko interacts regularly with parents Hiroshi and Sumire, grandparents Tomozo and Kotake, and classmates like Yoshiko. Her supportive, advisory role underscores her responsible nature.

In the movie’s art contest themed around favorite songs, Sakiko’s involvement mirrors her established family dynamics, consistently reflecting her orderly, occasionally exasperated yet caring role as the elder sister.