Tokiko Hishigata (菱形 朱鷺子, Hishigata Tokiko) is Sou's younger sister, a first-year high school student. She is intelligent and has the top grades in her grade, but she is physically weak and not good at sports. She and Mio have known each other since childhood and are classmates at the same high school.
Tokiko is a young girl with a long red hair braided in a tail.
Tokiko seems to be in love with Mio.
Tokiko joins Sou, Mio and Shinpei to visit the Summer Festival with them. Per Sou's request, she helps Mio to dress in yukata and they go pick up Shinpei. At the festival, Mio wonders what Sou and Shinpei are talking and panicking, Sou states they are discussing what they like more, butts or boobs, which makes Mio give Shinpei a strange look. Shinpei tries to deny it, but Tokiko states that's interesting conversation and reveals that Shinpei came in the bathroom while Mio was taking a bath, but Shinpei states he didn't see anything. Tokiko then wonders what Shinpei feels about Mio and he reveals he cares for her as a family. Mio then stops Tokiko from asking any other questions. Shinpei then sees something and runs and leaves the group. After the fireworks, Mio calls Shinpei and he rejoins them. They watch the ceremony and after it, Sou wants to confess to Mio. Tokiko tells Shinpei about it, but states it won't go well as Mio already loves someone else, but refuses to tell Shinpei who that is. After Sou confesses and Mio states he just wants to be friends, Ushio appears. Mio thinks she is a shadow and warns Shinpei, but Shinpei reveals that he himself is a shadow.
Other shadows appear and they start killing people. The real Shinpei appears and sees the blood. Tokiko starts crying and apologizes, saying that this wasn't why she dirtied her hands, but then she gets killed by a shadow.
Mio and Tokiko are hiding from the rain. Tokiko wonders if Mio will be going to the festival tomorrow, but Mio explains she doesn't have a yukata. Tokiko states she will gladly lend her one. Tokiko then wants a favor from Mio and asks her to stay with her tomorrow. A man then shows up, but seeing he isn't local, Tokiko wonders who he is. The man introduces himself as Miura from Wakayama's northern station and asks them if they knew the Kobayakawas.
Deep into the underground cave, Tokiko appears with two baby-like shadows and tells Shinpei's group to not do anything stupid or Ushio will die. Tokiko states she is there to retrieve a defective product and is glad that they brought Ushio. As she gets closer, Shinpei shoots at her shadow, pinning her multiple times with the nails, but Tokiko just laughs. Ushio tells Shinpei that Tokiko isn't a shadow. Tokiko wonders if Shinpei can kill humans and wants them to chat. Shinpei states they surrender and the shadows capture Ushio. Shinpei realizes that since they still haven't killed them, they won't harm Ushio for the moment and wonders if Tokiko will take them to her father. Sou wonders if she follows they father orders. Tokiko tells him its natural that he doesn't know anything, as he wasn't chosen by their father, but there is no need to keep it a secret anymore. Tokiko asks them to leave their stuff and follow her and she will lead them to Hiruko. Getting closer, Shinpei and the rest hear a rumble, and Tokiko explains its Hiruko's stomach. Tokiko states she accepted all and won't ask for forgiveness, but asks Shinpei to not let Mio know what he will see and learn. Tokiko then takes them to a large shadow that reaches the ceiling, and at its base is Heine, who states its 9 o'clock and time to eat.
Tokiko explains that Hiruko like to be called Heine and look like her, who is the first person she copied. Recently she had troubles walking and needed a new body, so she took Shiori. She explains that her family have been serving the shadows for generations and they bring the dead to her for she to eat them. As they bring Ushio's body, Tokiko states Ushio's death was a surprise to her and never expected she to team up with her own shadow in order to save Shiori. Sou can't accept this and yells at Tokiko, asking her where their father is. Tokiko yells back that its because he is like this that she had to carry everything herself. She had to do all of this, because if Heine dies, their mother would die too. Their mother wasn't cured and their father asked Heine to turn her into a Shadow, so she can live. When Shinpei and Ushio fight back, Tokiko states they can't win against the shadows. Ushio tells her that the Tokiko she knows won't stand for this and that Heine is using her to fill her belly. Soon, the shadow parent shows up and brings Mio as hostage. Tokiko is angry as they promised to not touch Mio. The shadow finds this foolish as all the humans on the island would be dying tomorrow at the festival. Tokiko wonders what he means as tomorrow Heine was supposed to have her final meal and heal her body, and then bring her mother back. The shadow shoots at Tokiko, but Sou gets in front and takes the bullet. The shadow is surprised, but states that their father already knows the tomorrow's plan, and then proceeds and shoots Tokiko.
Tokiko along Shinpei's friends is called to the elementary school. There Ushio shows them her memory of the previous loops. Shinpei asks them to help him and fight the shadows. Tokiko states they have no idea how many shadows are on the island and they don't really stand a chance, especially if Heine is looping back as well. However, she had already died in the other loops, so she decides to trust Shinpei and fight.
Shinpei explains to everyone else that he can only loop one more time as the time limit for the loop moves faster after each death.
When Heine and Shide come with shadows and they case Shinpei and Ushio, Heine orders shadow Mio to take out Ginjiro, however, Mio, Sou and Tokiko remain to protect him and fight Mio. Tokiko summons two baby-like shadows, Rosencrantz and Guildenstern, who push Mio away. When Heine notices the stray shadows, she orders them they to kill Tokiko as she isn't their master, however the shadows refuse to listen to Heine as their connection with Heine had been severed previously by Ushio. Eventually they manage to defeat Mio and pin her with the nailgun and later ask Ushio to turn her one of them.
After making Shadow Mio their ally, Shinpei questions her and they learn that all shadows except Heine, can give "birth" to only one shadow and that shadow cannot give "birth". Shinpei then decides they go speak with Seido Hishigata as he seems to know Heine's plan. However, reaching the hospital, they see all items and furniture being erased. Tokiko remains in the car with Ginjiro and Mio. She had let Shadow Mio copy her and join the group. Tokiko also wanted Shadow Mio to learn everything about her and her feelings.
- The name Tokiko means "crested ibis" (朱鷺) (toki) and "child" (子) (ko).
- Part of the name Toki can also mean "vermilion red" (朱) (to) and "heron" (鷺) (ki) separately.
- Tokiko's surname Hishigata means "Rhombus, diamond shape" (菱形).