Asako Tsukishima is the wife of Seiya Tsukishima and mother to Shiho and Shizuku Tsukishima. She possesses brown hair and black eyes, often seen in a light purple turtleneck paired with a beige cardigan. Her given name, meaning "morning child" (combining "Asa" for morning and "ko" for child), and surname "Tsukishima" (signifying "moon island") reflect her heritage.

Within the family, Asako actively participates in conversations regarding Shizuku's academic performance and future plans, especially when Shizuku's focus on writing causes her school grades to slip. While expressing concern over this decline, Asako ultimately supports her daughter's creative pursuits, joining family decisions to trust Shizuku during her dedicated writing period. She is also present when Shizuku later announces her intention to resume studying for high school entrance exams, demonstrating her ongoing involvement in Shizuku's education.