Kayo Hinazuki is a ten-year-old girl and the first victim of the serial killer/kidnapper. She went missing on the 2nd of March 1988. Her body was found a few days later once the snow had thawed.
She is abused by her mother, a fact which all the adults around her are aware of but are unable to do anything about. Child Protective services had attempted to deal with the situation but were unable to gain any concrete proof or even set up a meeting.
Due to this abuse, she’s a social outcast at school, preferring to distance herself from other people, hoping that if she wears the mask of apathy long enough, it will become real. After school, she spends her time mostly alone at a local park until 6 P.M., to avoid going home and facing her mother.
After returning to his childhood, Satoru attempts to get close to her in order to avoid her being kidnapped, reasoning that she was taken because she was always seen alone in the park. It’s during this time she reveals that she’s only pretending to be apathetic and that she knows he’s wearing his own mask.
This time around, she spends the 2nd of March with Satoru celebrating both his and her birthday and consequently does not get kidnapped. However, she still dies the following day.
She had been beaten near to death and locked inside a storage room. Her killer took her out of the storage room after she stopped shivering, placed her inside an industrial freezer and sprayed her with water until she froze to death, the killer waited until resuscitation was impossible and returned her body to the storage room. This was where she was discovered.
On the next attempt to save her, events unfold as before up until she leaves the birthday party. She is “kidnapped” by Satoru and hides out in an old broken down bus with the help from their friends, Kenya and Hiromi. During her stay there, a stranger appears and angrily kicks a box of what later is found to be kidnapping equipment but doesn’t notice Kayo is there from where she’s hiding behind a curtain that separates the bus into two parts. After this incident occurs, she stays the night at Satoru’s home.
Following a confrontation with her mother, involving Satoru and his mother, CPS placed her into the custody of her maternal grandmother.
Kayo had developed feelings for Satoru and it shocked her greatly when Yashiro announced to the class that Satoru got into accident. She often visited Satoru in the hospital, praying for him to wake up soon. Fujinuma Sachiko, Satoru’s mom, couldn’t bear to see Kayo wasting her life like that. She transported him to a hospital in Chiba without informing Kayo, leaving only a letter of thanks for her support, but with a request for Kayo to cherish her “present” so she could have a bright future.
In the future, Kayo married Sugita Hiromi. When Satoru awakened from coma she visited him with her son Mirai.