Sayoko Kurosaki exhibits a notably dark and irresponsible personality. Estranged from her wealthy sculptor father after eloping with the family gardener instead of accepting an arranged marriage, she faced disownment and financial hardship. Widowed, she raises her adopted daughter Asami Kurosaki alone. They endure extreme poverty in room #5 of Narutaki-sou, using cardboard boxes as furniture and bedding. Sayoko chronically neglects household duties, sleeping excessively and forcing middle-schooler Asami to manage expenses and chores. Despite her apparent uselessness, she genuinely cares for Asami and expresses a desire for their long-term happiness together. Her favorite food is Mizuyōkan.

Her portrayal diverges between media: the manga depicts inept, unsuccessful suicidal tendencies, while the anime omits self-destructive elements, focusing solely on lethargy and irresponsibility. Both versions center on her dependent relationship with Asami. Sayoko experiences no character development, remaining consistently unreliable without financial improvement or paternal reconciliation. The epilogue shows her still residing at Narutaki-sou with Asami, maintaining their established dynamic. Physically, she has black hair, brown eyes (though some sources list red), and an adult appearance.