|Appearance||Period 42: Best Friend Chocolate|
Chiyoko is a thin woman whose features make her age ambiguous. She has long navel-length white hair and long bangs that shadows her face. Her attire resembles a high school uniform; a buttoned top with a trench-coat, pleat skirt, socks, and loafers. She wears a black muffler or scarf.
As a child Chiyoko had been extremely shy and couldn't talk to people, so she didn't have friends and wasn't able to approach them. She is silence, using gestures in order to speak to people and no longer hesitates to approach.
Once school ended, Hina began to make her way home while thinking about eating Mari's chocolate when she ran into Chiyoko-san. She had been alarmed by her ghostly appearance, and while wondering why she would be there, Chiyoko held up a wrapped present box for her. She shoved it into the confused Hina's hands and vanished as other people began to appear, and when Hina felt uncomfortable she tossed the present aside.
The following day Chiyoko had sneaked into the school and somehow planted the wrapped present into Hina's shoe locker- much to her shock when she opened it. Mari suggested she open it after seeing how concerned she looked and she did, seeing harmless looking chocolate inside. But still shaken, Hina freaked out and tossed it aside before running away. When Mari followed her, Hina explained what happened the prior day and a male classmate joined them, recognizing it as a gift from Chiyoko-san. The girls were confused, and he explains that a mysterious woman, Chiyoko-san, goes around delivering chocolate to girls. But they're only girls from their school. Since she was little Chiyoko wasn't able to make any friends due to her dark personality and quiet nature. But desperate for friendship she started to make chocolate and gives it out. It's said that if someone accepts her chocolate, she will follow them and eventually take them away.
Chiyoko has struck again when class starts. Hina sits down and was horrified to find the re-wrapped chocolate hiding in her desk and her freak out during class not only alerted the rest of class, but the teaching staff as well. She handed the chocolate over and they set up a heavy patrol system to keep an eye on her to make sure she and everyone else will be safe; but Hina is unable to shake her sudden loneliness when her classmates start avoiding her out of fear.
The girls play outside for a short while until they hear a sudden cry of alarm, and they join their classmates in the nearby hallway to see that Chiyoko somehow delivered chocolate to one of the teachers and now they are panicking. As it dons on her that she must be in the school somewhere, the students start to turn on her and blame Hina for "accepting the chocolate" to begin with. As Mari defends her, everyone is overwhelmed by fright when they suddenly find Chiyoko watching Hina from the window opposite of where they stand. She gestures for Hina but she refuses knowing it could be to kidnap her, and she takes off after the other students abandon Hina- along with Mari, leaving her stunned as the teachers return, having heard all the noise.
Running away from school later in the story, Hina remains angry at Mari until she realizes that she sent her a text during the time they spent apart. Realizing she gravely injured her friend she decides she must make amends and find her, but before Hina can leave she was horrified to discover that Chiyoko broke through her door locks and is waiting for her. Chiyoko approaches her and forces the chocolate into her mouth until she loses consciousness.
Later that day, Mari is shown in the hospital in a panic when she isn't able to get in touch with Hina. Then the nurse returns and reveals a wrapped present that had been left for her by a "strange woman".