Kayo Hinazuki is one of the three original victims in a serial kidnapping and killing commited by Gaku Yashiro. The other two victims being Hiromi Sugita and Aya Nakanishi. She is one of Satoru Fujinuma's primary school classmate and is a loner due to her mysterious family life.
Kayo doesn't have much of a presence in class. Prior to becoming friends with Satoru's group, she didn't have any to call her own and barely spoke to anyone. She considered Satoru and herself as "fakes", as both of them distanced themselves from others, were often irritated by someone's behaviors and had trust issues. This stemmed from her abusive household, as Hinazuki believed that if she numbed her emotions, her mother couldn't inflict any more pain onto her. She often dreamed of escaping her cruel life and living on an island far away from society where she could be free. She is extremely blunt and tends to call people idiots, though it's usually directed at Satoru.
Following Satoru's rerun in an attempt to save her, Kayo starts to open up to him and is initially uncomfortable of his generosity. When she stays over at Fujinuma's house, Hinazuki breaks down in tears at Sachiko's kindness, having never experienced an act of altruism. Following Satoru's comatose, Kayo frequently went to visit him in the hospital and helped out his mother. The two developed a close relationship and Kayo came to think of Sachiko as her own mother. As an adult, Kayo tells Satoru she managed to obtain happiness and is shown with a smile gently holding her child.
As a loner, Kayo made her an easy target to kidnap. In an attempt to prevent her kidnapping, Satoru desperately tries to befriend her when he returned to the past.
Kayo's mother abused her quite a lot throughout her life. Many injuries included suffocation, bruises and other tortures. When Kayo first met Satoru during the 18 year "Revival" she asked Satoru to kill someone for her (meaning it as a' joke'), however, she had actually wanted him to kill her mother, out of her depression from the abuse her mother gave her.
After Satoru wakes up, She visits him with her son. She reflects on her discomfort of leaving him behind and is chided by Satoru in turn.
|“||Are you stupid? (JP: Baka na no?)||„|
|“||Everybody is fake, living in their fake lives.||„|
|~ Kayo to Satoru|
|“||Can you kill someone for my sake?||„|
|~ Kayo to Satoru|
|“||When I get bigger, big enough to go somewhere by myself, I want to go to a land that’s far away. I want to go to a faraway island. I want to go to an island that has no people. I want to go to an island that has no pain or sadness. On that island, I can climb a tree when I want to climb, swim in the sea when I want to swim, and sleep when I want to sleep. When I think about the town without me, I feel a sense of relief. I want to go far, far away.||„|
|~ Kayo's poem; The Town Without Me|
- Kayo always use the phrase "Are you stupid?" when talking to Satoru. This phrase is also used by Airi Katagiri, which gives him a shock when he hears that, giving a hint that Airi is likely a reincarnation of Kayo for him.
- In the manga version, Kayo is not transferred to a new school after the incident but in the anime version, she did. It creates a little confusion in the end as Kayo marries Hiromi which is has a slight chance to happen due to this.