Kiyomi Sakura is a supporting character encountered by Squid Girl during one of her early attempts at mischief on land. Their first meeting occurred when Squid Girl planned to prank a family by ringing their doorbell and running away. She was caught by Chizuru Aizawa, who happened to know the family. In an attempt to avoid trouble, Squid Girl claimed she was waiting for a friend named Kiyomi. By coincidence, Kiyomi arrived at that exact moment, leading to an introduction and the beginning of their friendship.

In terms of appearance, Kiyomi is an average-height middle school girl who appears to be around the same age as Squid Girl. She has brown hair which she typically wears in two pigtails, brown eyes, and large round glasses. Her usual attire is her middle school uniform, though when she visits Squid Girl at the Lemon beach house she wears a plain yellow top. Her bathing suit is a frilly pink bikini.

Kiyomi has a very sweet, calm, and kind personality. She is a loyal friend who patiently puts up with Squid Girl's often eccentric and intrusive antics. Her gentle and unassuming nature allows her to get along with almost everyone she meets, and it was this quality that charmed Squid Girl during their first encounter.

As Squid Girl's closest human friend, Kiyomi plays a significant role in bridging the gap between the sea-dwelling invader and the human world. She recruits Squid Girl to play on her middle school baseball team when a player is missing, an experience that allows Squid Girl to make even more friends among Kiyomi's classmates. Later, some of these schoolmates go on to form the Squid Girl Invasion Club, further expanding the circle of people who appreciate Squid Girl's unique presence.

Kiyomi's key relationships center around Squid Girl, whom she considers a best friend. This close bond is a source of intense jealousy for Sanae Nagatsuki, who has an obsessive crush on Squid Girl. Kiyomi is also friends with her other middle school peers, including Tomomi Mochizuki, Ayano Watanabe, and Yuka Nishimura.

Throughout the story, Kiyomi develops primarily by integrating Squid Girl into her existing social life, helping the marine invader find a place among ordinary human students. While Kiyomi does not possess any combat abilities or supernatural powers, her notable ability lies in her social grace. She makes friends with ease and acts as a calming influence, often smoothing over situations that Squid Girl's impulsive behavior might otherwise complicate. Her primary role is to serve as a kind and accepting human friend who shows Squid Girl that not all land dwellers are enemies to be conquered, but potential companions to be valued.